Catalysts

ABSTRACT

Wherein M1 and M2 are independently selected from Zn(II), Cr(II), Co(II), Cu(II), Mn(II), Ni(II), Mg(II), Fe(II), Ti(II), V(II), Cr(III)-X, Co(III)-X, Ni(III)-X, Mn(III)-X, Fe(III)-X, Ca(II), Ge(II), AI(III)-X, Ti(III)-X, V(III)-X, Ge(IV)-(X)2 or Ti(IV)-(X)2. R3A is different from R3B; and/or at least one occurrence of E3, E4, E5 and E6 is different to a remaining occurrence of E3, E4, E5 and E6. A ligand, a process of asymmetric N-substitution of a symmetrical ligand and a process for the reaction of: (i) carbon dioxide with an epoxide; (ii) an epoxide and an anhydride; and/or (iii) a lactide and/or a lactone, in the presence of a catalyst is also described.

FIELD OF THE INVENTION

The present invention relates to the field of polymerisation catalysts,and systems comprising said catalysts for polymerising carbon dioxideand an epoxide, a lactide and/or lactone, and/or an epoxide and ananhydride.

BACKGROUND

Environmental and economic concerns associated with depleting oilresources have triggered a growing interest in the chemical conversionof carbon dioxide (CO₂), so as to enable its use as a renewable carbonsource. CO₂ is, despite its low reactivity, a highly attractive carbonfeedstock, as it is inexpensive, virtually non-toxic, abundantlyavailable in high purity and non-hazardous. Therefore, CO₂ could be apromising substitute for substances such as carbon monoxide, phosgene orother petrochemical feedstocks in many processes. One of the developingapplications of CO₂ is the copolymerization with epoxides to yieldaliphatic polycarbonates. The development of effective catalysts to makesuch a process profitable is the subject of continuous research.

In WO2009/130470, the contents of which are incorporated herein byreference in their entirety, the copolymerisation of an epoxide with CO₂using a catalyst of a class represented by formula (I) was described:

WO2013/034750, the contents of which are incorporated herein byreference in their entirety, discloses the copolymerisation of anepoxide with CO₂ in the presence of a chain transfer agent using acatalyst of a class represented by formula (I):

Various compounds according to formula (I) above were tested for theirability to catalyse the reaction between different epoxides and carbondioxide.

In each of these tested catalysts, both occurrences of R₃ were the sameand all occurrence of R₄ were the same (referred to hereinafter assymmetric catalysts).

Among the epoxides employed in the copolymerization reactions of theprior art, cyclohexene oxide (CHO) received special interest, as theproduct, poly(cyclohexene carbonate) (PCHC) shows a high glasstransition temperature and reasonable tensile strength. Ethylene oxide,propylene oxide and butylene oxide have also received interest as theyproduce polymers (polyalkylene carbonates, such as PPC) with elastomericproperties which are useful in many applications e.g. films.

The inventors have now surprisingly found that the asymmetric catalystsreferred to herein represent a novel and inventive means of catalysingthe polymerisation of carbon dioxide with various monomers to produceuseful polymer products with good activity and selectivity.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda catalyst of formula (I):

wherein:M₁ and M₂ are independently selected from Zn(II), Cr(II), Co(II),Cu(II), Ni(II), Mn(II), Mg(II), Fe(II), Ti(II), V(II), Cr(III)-X,Co(III)-X, Ni(III)-X, Mn(III)-X, Fe(III)-X, Ca(II), Ge(II), AI(III)-X,Ti(III)-X, V(III)-X, Ge(IV)-(X)₂ or Ti(IV)-(X)₂;R₁ and R₂ are independently selected from hydrogen, halide, a nitrogroup, a nitrile group, an imine, an amine, an ether group, a silylgroup, a silyl ether group, a sulfoxide group, a sulfonyl group, asulfinate group or an acetylide group or an optionally substitutedalkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy,alkylthio, arylthio, alicyclic or heteroalicyclic group;R_(3A) and R_(3B) are independently selected from optionally substitutedalkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene,heteroalkynylene, arylene, heteroarylene or cycloalkylene, whereinalkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene andheteroalkynylene, may optionally be interrupted by aryl, heteroaryl,alicyclic or heteroalicyclic;R₅ is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl;E₁ is C, E₂ is O, S or NH or E, is N and E₂ is O;E₃, E₄, E₅ and E₆ are each independently selected from N, NR₄, O and S,wherein when any of E₃, E₄, E₅ or E₆ are N,

is

, and wherein when any of E₃, E₄, E₅ or E₆ are NR₄, O or S,

is

; R₄ is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl;X is independently selected from OC(O)R^(x), OSO₂R^(x), OSOR^(x),OSO(R^(x))₂, S(O)R^(x), OR^(x), phosphinate, halide, nitrate, hydroxyl,carbonate, amino, amido or optionally substituted aliphatic,heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl;R_(x) is independently hydrogen, or optionally substituted aliphatic,haloaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,alkylaryl or heteroaryl; andG is absent or independently selected from a neutral or anionic donorligand which is a Lewis base;and wherein:

-   -   i) R_(3A) is different from R_(3B); and/or    -   ii) at least one occurrence of E₃, E₄, E₅ and E₆ is different to        a remaining occurrence of E₃, E₄, E₅ and E₆.

According to a second aspect of the present invention, there is provideda ligand of formula (II):

wherein:R₁ and R₂ are independently selected from hydrogen, halide, a nitrogroup, a nitrile group, an imine, an amine, an ether group, a silylgroup, a silyl ether group, a sulfoxide group, a sulfonyl group, asulfinate group or an acetylide group or an optionally substitutedalkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy,alkylthio, arylthio, alicyclic or heteroalicyclic group;R_(3A) and R_(3B) are independently selected from optionally substitutedalkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene,heteroalkynylene, arylene, heteroarylene or cycloalkylene, whereinalkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene andheteroalkynylene, may optionally be interrupted by aryl, heteroaryl,alicyclic or heteroalicyclic;R₅ is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl;E₁ is C, E₂ is OY, S or NH or E, is N and E₂ is O;Y is hydrogen or an alkali metal;E₃, E₄, E₅ and E₆ are each independently selected from N, NR₄, O and S,wherein when any of E₃, E₄, E₅ or E₆ are N,

is

, and wherein when any of E₃, E₄, E₅ or E₆ are NR₄, O or S,

is

; R₄ is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl;

-   -   and wherein:    -   i) R_(3A) is different from R_(3B); and/or    -   ii) at least one occurrence of E₃, E₄, E₅ and E₆ is different to        a remaining occurrence of E₃, E₄, E₅ and E₆.

In a third aspect of the present invention, the invention extends tomethods of preparation of ligands, complexes and catalysts according tothe second aspect and first aspect respectively or as otherwise definedherein.

In a fourth aspect of the present invention, there is provided a processof asymmetric N-substitution of a symmetrical ligand having atetraaminophenol coordination sphere, the process comprising thefollowing steps:

-   -   a) protecting the amino groups of the coordination sphere of the        symmetrical ligand with an optionally substituted alkylene;    -   b) asymmetrically N-substituting one or more of the protected        amino groups of the product of step (a) with a substituent.

In a fifth aspect of the invention, there is provided a process for thereaction of (i) carbon dioxide with an epoxide, (ii) an anhydride and anepoxide, and/or (iii) a lactide and/or a lactone in the presence of acatalyst according to the first aspect, optionally in the presence of achain transfer agent.

The sixth aspect of the invention provides a product of the process ofthe fifth aspect of the invention.

Definitions

For the purpose of the present invention, an aliphatic group is ahydrocarbon moiety that may be straight chain or branched and may becompletely saturated, or contain one or more units of unsaturation, butwhich is not aromatic. The term “unsaturated” means a moiety that hasone or more double and/or triple bonds. The term “aliphatic” istherefore intended to encompass alkyl, alkenyl or alkynyl groups, andcombinations thereof. An aliphatic group is preferably a C₁₋₂₀ aliphaticgroup, that is, an aliphatic group with 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,11, 12, 13, 14, 15, 16, 17, 18, 19 or 20 carbon atoms. Preferably, analiphatic group is a C₁₋₁₅aliphatic, more preferably a C₁₋₁₂aliphatic,more preferably a C₁₋₁₀aliphatic, even more preferably a C₁₋₈aliphatic,such as a C₁₋₆aliphatic group.

An alkyl group is preferably a “C₁₋₂₀ alkyl group”, that is an alkylgroup that is a straight or branched chain with 1 to 20 carbons. Thealkyl group therefore has 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,15, 16, 17, 18, 19 or 20 carbon atoms. Preferably, an alkyl group is aC₁₋₁₅alkyl, preferably a C₁₋₁₂alkyl, more preferably a C₁₋₁₀alkyl, evenmore preferably a C₁₋₈alkyl, even more preferably a C₁₋₆alkyl group.Specifically, examples of “C₁₋₂₀ alkyl group” include methyl group,ethyl group, n-propyl group, iso-propyl group, n-butyl group, iso-butylgroup, sec-butyl group, tert-butyl group, n-pentyl group, n-hexyl group,n-heptyl group, n-octyl group, n-nonyl group, n-decyl group, n-undecylgroup, n-dodecyl group, n-tridecyl group, n-tetradecyl group,n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecylgroup, n-nonadecyl group, n-eicosyl group, 1,1-dimethylpropyl group,1,2-dimethylpropyl group, 2,2-dimethylpropyl group, 1-ethylpropyl group,n-hexyl group, 1-ethyl-2-methylpropyl group, 1,1,2-trimethylpropylgroup, 1-ethylbutyl group, 1-methylbutyl group, 2-methylbutyl group,1,1-dimethylbutyl group, 1,2-dimethylbutyl group, 2,2-dimethylbutylgroup, 1,3-dimethylbutyl group, 2,3-dimethylbutyl group, 2-ethylbutylgroup, 2-methylpentyl group, 3-methylpentyl group and the like.

Alkenyl and alkynyl groups are preferably “C₂₋₂₀alkenyl” and“C₂₋₂₀alkynyl”, more preferably “C₂₋₁₅alkenyl” and “C₂₋₁₅alkynyl”, evenmore preferably “C₂₋₁₂alkenyl” and “C₂₋₁₂alkynyl”, even more preferably“C₂₋₁₀alkenyl” and “C₂₋₁₀alkynyl”, even more preferably “C₂₋₈alkenyl”and “C₂₋₈alkynyl”, most preferably “C₂₋₆alkenyl” and “C₂₋₆alkynyl”groups, respectively. Alkene and alkyne should be understoodaccordingly.

A heteroaliphatic group is an aliphatic group as described above, whichadditionally contains one or more heteroatoms. Heteroaliphatic groupstherefore preferably contain from 2 to 21 atoms, preferably from 2 to 16atoms, more preferably from 2 to 13 atoms, more preferably from 2 to 11atoms, more preferably from 2 to 9 atoms, even more preferably from 2 to7 atoms, wherein at least one atom is a carbon atom. Particularlypreferred heteroatoms are selected from O, S, N, P and Si. Whenheteroaliphatic groups have two or more heteroatoms, the heteroatoms maybe the same or different.

An alicyclic group is a saturated or partially unsaturated cyclicaliphatic monocyclic or polycyclic (including fused, bridging andspiro-fused) ring system which has from 3 to 20 carbon atoms, that is analicyclic group with 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,17, 18, 19 or 20 carbon atoms. Preferably, an alicyclic group has from 3to 15, more preferably from 3 to 12, even more preferably from 3 to 10,even more preferably from 3 to 8 carbon atoms, even more preferably from3 to 6 carbons atoms. The term “alicyclic” encompasses cycloalkyl,cycloalkenyl and cycloalkynyl groups. It will be appreciated that thealicyclic group may comprise an alicyclic ring bearing one or morelinking or non-linking alkyl substituents, such as —CH₂-cyclohexyl.Specifically, examples of the C₃₋₂₀ cycloalkyl group includecyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyland cyclooctyl.

A heteroalicyclic group is an alicyclic group as defined above whichhas, in addition to carbon atoms, one or more ring heteroatoms, whichare preferably selected from O, S, N, P and Si. Heteroalicyclic groupspreferably contain from one to four heteroatoms, which may be the sameor different. Heterocyclic groups preferably contain from 5 to 20 atoms,more preferably from 5 to 14 atoms, even more preferably from 5 to 12atoms.

An aryl group is a monocyclic or polycyclic ring system having from 5 to20 carbon atoms. An aryl group is preferably a “C₆₋₁₂ aryl group” and isan aryl group constituted by 6, 7, 8, 9, 10, 11 or 12 carbon atoms andincludes condensed ring groups such as monocyclic ring group, orbicyclic ring group and the like. Specifically, examples of “C₆₋₁₀ arylgroup” include phenyl group, biphenyl group, indenyl group, naphthylgroup or azulenyl group and the like. It should be noted that condensedrings such as indan and tetrahydro naphthalene are also included in thearyl group.

A heteroaryl group is an aryl group having, in addition to carbon atoms,from one to four ring heteroatoms which are preferably selected from O,S, N, P and Si. A heteroaryl group preferably has from 5 to 20, morepreferably from 5 to 14 ring atoms. Specifically, examples of aheteroaryl group include pyridine, imidazole, methylimidazole anddimethylaminopyridine.

Examples of alicyclic, heteroalicyclic, aryl and heteroaryl groupsinclude but are not limited to cyclohexyl, phenyl, acridine,benzimidazole, benzofuran, benzothiophene, benzoxazole, benzothiazole,carbazole, cinnoline, dioxin, dioxane, dioxolane, dithiane, dithiazine,dithiazole, dithiolane, furan, imidazole, imidazoline, imidazolidine,indole, indoline, indolizine, indazole, isoindole, isoquinoline,isoxazole, isothiazole, morpholine, napthyridine, oxazole, oxadiazole,oxathiazole, oxathiazolidine, oxazine, oxadiazine, phenazine,phenothiazine, phenoxazine, phthalazine, piperazine, piperidine,pteridine, purine, pyran, pyrazine, pyrazole, pyrazoline, pyrazolidine,pyridazine, pyridine, pyrimidine, pyrrole, pyrrolidine, pyrroline,quinoline, quinoxaline, quinazoline, quinolizine, tetrahydrofuran,tetrazine, tetrazole, thiophene, thiadiazine, thiadiazole, thiatriazole,thiazine, thiazole, thiomorpholine, thianaphthalene, thiopyran,triazine, triazole, and trithiane.

The term “halide” or “halogen” are used interchangeably and, as usedherein mean a fluorine atom, a chlorine atom, a bromine atom, an iodineatom and the like, preferably a fluorine atom, a bromine atom or achlorine atom, and more preferably a fluorine atom.

A haloalkyl group is preferably a “C₁₋₂₀ haloalkyl group”, morepreferably a “C₁₋₁₅ haloalkyl group”, more preferably a “C₁₋₁₂ haloalkylgroup”, more preferably a “C₁₋₁₀ haloalkyl group”, even more preferablya “C₁₋₈ haloalkyl group”, even more preferably a “C₁₋₆ haloalkyl group”and is a C₁₋₂₀ alkyl, a C₁₋₁₅ alkyl, a C₁₋₁₂ alkyl, a C₁₋₁₀ alkyl, aC₁₋₈ alkyl, or a C₁₋₆ alkyl group, respectively, as described abovesubstituted with at least one halogen atom, preferably 1, 2 or 3 halogenatom(s). Specifically, examples of “C₁₋₂₀ haloalkyl group” includefluoromethyl group, difluoromethyl group, trifluoromethyl group,fluoroethyl group, difluroethyl group, trifluoroethyl group,chloromethyl group, bromomethyl group, iodomethyl group and the like.

An alkoxy group is preferably a “C₁₋₂₀ alkoxy group”, more preferably a“C₁₋₁₅ alkoxy group”, more preferably a “C₁₋₁₂ alkoxy group”, morepreferably a “C₁₋₁₀ alkoxy group”, even more preferably a “C₁₋₈ alkoxygroup”, even more preferably a “C₁₋₆ alkoxy group” and is an oxy groupthat is bonded to the previously defined C₁₋₂₀ alkyl, C₁₋₁₅ alkyl, C₁₋₁₂alkyl, C₁₋₁₀ alkyl, C₁₋₈ alkyl, or C₁₋₆ alkyl group respectively.Specifically, examples of “C₁₋₂₀ alkoxy group” include methoxy group,ethoxy group, n-propoxy group, iso-propoxy group, n-butoxy group,iso-butoxy group, sec-butoxy group, tert-butoxy group, n-pentyloxygroup, iso-pentyloxy group, sec-pentyloxy group, n-hexyloxy group,iso-hexyloxy group, n-hexyloxy group, n-heptyloxy group, n-octyloxygroup, n-nonyloxy group, n-decyloxy group, n-undecyloxy group,n-dodecyloxy group, n-tridecyloxy group, n-tetradecyloxy group,n-pentadecyloxy group, n-hexadecyloxy group, n-heptadecyloxy group,n-octadecyloxy group, n-nonadecyloxy group, n-eicosyloxy group,1,1-dimethylpropoxy group, 1,2-dimethylpropoxy group,2,2-dimethylpropoxy group, 2-methylbutoxy group, 1-ethyl-2-methylpropoxygroup, 1,1,2-trimethylpropoxy group, 1,1-dimethylbutoxy group,1,2-dimethylbutoxy group, 2,2-dimethylbutoxy group, 2,3-dimethylbutoxygroup, 1,3-dimethylbutoxy group, 2-ethylbutoxy group, 2-methylpentyloxygroup, 3-methylpentyloxy group and the like.

An aryloxy group is preferably a “C₅₋₂₀ aryloxy group”, more preferablya “C₆₋₁₂ aryloxy group”, even more preferably a “C₆₋₁₀ aryloxy group”and is an oxy group that is bonded to the previously defined C₅₋₂₀ aryl,C₆₋₁₂ aryl, or C₆₋₁₀ aryl group respectively.

An alkylthio group is preferably a “C₁₋₂₀ alkylthio group”, morepreferably a “C₁₋₁₅ alkylthio group”, more preferably a “C₁₋₁₂ alkylthiogroup”, more preferably a “C₁₋₁₀ alkylthio group”, even more preferablya “C₁₋₈ alkylthio group”, even more preferably a “C₁₋₆ alkylthio group”and is a thio (—S—) group that is bonded to the previously defined C₁₋₂₀alkyl, C₁₋₁₅ alkyl, C₁₋₁₂ alkyl, C₁₋₁₀ alkyl, C₁₋₈ alkyl, or C₁₋₆ alkylgroup respectively.

An arylthio group is preferably a “C₅₋₂₀ arylthio group”, morepreferably a “C₆₋₁₂ arylthio group”, even more preferably a “C₆₋₁₀arylthio group” and is an thio (—S—) group that is bonded to thepreviously defined C₅₋₂₀ aryl, C₆₋₁₂ aryl, or C₆₋₁₀ aryl grouprespectively.

An alkylaryl group is preferably a “C₆₋₁₂ aryl C₁₋₂₀ alkyl group”, morepreferably a preferably a “C₆₋₁₂ aryl C₁₋₁₆ alkyl group”, even morepreferably a “C₆₋₁₂ aryl C₁₋₆ alkyl group” and is an aryl group asdefined above bonded at any position to an alkyl group as defined above.The point of attachment of the alkylaryl group to a molecule may be viathe alkyl portion and thus, preferably, the alkylaryl group is —CH₂-Phor —CH₂CH₂-Ph. An alkylaryl group can also be referred to as “aralkyl”.

A silyl group is preferably a group —Si(R_(s))₃, wherein each R_(s) canbe independently an aliphatic, heteroaliphatic, alicyclic,heteroalicyclic, aryl or heteroaryl group as defined above. In certainembodiments, each R_(s) is independently an unsubstituted aliphatic,alicyclic or aryl. Preferably, each R_(s) is an alkyl group selectedfrom methyl, ethyl or propyl.

A silyl ether group is preferably a group OSi(R₆)₃ wherein each R₆ canbe independently an aliphatic, heteroaliphatic, alicyclic,heteroalicyclic, aryl or heteroaryl group as defined above. In certainembodiments, each R₆ can be independently an unsubstituted aliphatic,alicyclic or aryl.

Preferably, each R₆ is an optionally substituted phenyl or optionallysubstituted alkyl group selected from methyl, ethyl, propyl or butyl(such as n-butyl or tert-butyl (tertiary butyl)). Exemplary silyl ethergroups include OSi(Me)₃, OSi(Et)₃, OSi(Ph)₃, OSi(Me)₂(tertiary butyl),OSi(tertiary butyl)₃ and OSi(Ph)₂(tertiary butyl).

A nitrile group (also referred to as a cyano group) is a group CN.

An imine group is a group —CRNR, preferably a group —CHNR₇ wherein R₇ isan aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl orheteroaryl group as defined above. In certain embodiments, R₇ isunsubstituted aliphatic, alicyclic or aryl. Preferably R₇ is an alkylgroup selected from methyl, ethyl or propyl.

An acetylide group contains a triple bond —C≡C—R₉, preferably wherein R₉can be hydrogen, an aliphatic, heteroaliphatic, alicyclic,heteroalicyclic, aryl or heteroaryl group as defined above. For thepurposes of the invention when R₉ is alkyl, the triple bond can bepresent at any position along the alkyl chain. In certain embodiments,R₉ is unsubstituted aliphatic, alicyclic or aryl. Preferably R₉ ismethyl, ethyl, propyl or phenyl.

An amino group is preferably —NH₂, —NHR₁₀ or —N(R₁₀)₂ wherein R₁₀ can bean aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, a silylgroup, aryl or heteroaryl group as defined above. It will be appreciatedthat when the amino group is N(R₁₀)₂, each R₁₀ group can be the same ordifferent. In certain embodiments, each R₁₀ is independently anunsubstituted aliphatic, alicyclic, silyl or aryl. Preferably R₁₀ ismethyl, ethyl, propyl, SiMe₃ or phenyl.

An amido group is preferably —NR₁₁C(O)— or —C(O)—NR₁₁— wherein R₁₁ canbe hydrogen, an aliphatic, heteroaliphatic, alicyclic, heteroalicyclic,aryl or heteroaryl group as defined above. In certain embodiments, R₁₁is unsubstituted aliphatic, alicyclic or aryl. Preferably R₁₁ ishydrogen, methyl, ethyl, propyl or phenyl. The amido group may beterminated by hydrogen, an aliphatic, heteroaliphatic, alicyclic,heteroalicyclic, aryl or heteroaryl group.

An ester group is preferably —OC(O)R₁₂— or —C(O)OR₁₂— wherein R₁₂ can behydrogen, an aliphatic, heteroaliphatic, alicyclic, heteroalicyclic,aryl or heteroaryl group as defined above. In certain embodiments, R₁₂is unsubstituted aliphatic, alicyclic or aryl. Preferably R₁₂ ishydrogen, methyl, ethyl, propyl or phenyl. The ester group may beterminated by hydrogen, an aliphatic, heteroaliphatic, alicyclic,heteroalicyclic, aryl or heteroaryl group.

A sulfoxide is preferably —S(O)R₁₃ and a sulfonyl group is preferably—S(O)₂R₁₃ wherein R₁₃ can be hydrogen, an aliphatic, heteroaliphatic,alicyclic, heteroalicyclic, aryl or heteroaryl group as defined above.In certain embodiments, R₁₃ is unsubstituted aliphatic, alicyclic oraryl. Preferably R₁₃ is hydrogen, methyl, ethyl, propyl or phenyl.

A carboxylate group is preferably —OC(O)R₁₄, wherein R₁₄ can behydrogen, an aliphatic, heteroaliphatic, alicyclic, heteroalicyclic,aryl or heteroaryl group as defined above. In certain embodiments, R₁₄is unsubstituted aliphatic, alicyclic or aryl. Preferably R₁₄ ishydrogen, methyl, ethyl, propyl, butyl (for example n-butyl, isobutyl ortert-butyl), phenyl, pentafluorophenyl, pentyl, hexyl, heptyl, octyl,nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl,hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, trifluoromethyl oradamantyl.

In an -alkylC(O)OR₁₉ or -alkylC(O)R₁₉ group, R₁₉ can be hydrogen, analiphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl orheteroaryl group as defined above. In certain embodiments, R₁₉ isunsubstituted aliphatic, alicyclic or aryl. Preferably R₁₉ is hydrogen,methyl, ethyl, propyl, butyl (for example n-butyl, isobutyl ortert-butyl), phenyl, pentafluorophenyl, pentyl, hexyl, heptyl, octyl,nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl,hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, trifluoromethyl oradamantyl.

An acetamide is preferably MeC(O)N(R₁₅)₂ wherein R₁₅ can be hydrogen, analiphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl orheteroaryl group as defined above. In certain embodiments, R₁₅ isunsubstituted aliphatic, alicyclic or aryl. Preferably R₁₅ is hydrogen,methyl, ethyl, propyl or phenyl.

A phosphinate group is preferably a group —OP(O)(R₁₆)₂ or —P(O)(OR₁₆)wherein each R₁₆ is independently selected from hydrogen, or analiphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl orheteroaryl group as defined above. In certain embodiments, R₁₆ isaliphatic, alicyclic or aryl, which are optionally substituted byaliphatic, alicyclic, aryl or C₁₋₆alkoxy. Preferably R₁₆ is optionallysubstituted aryl or C₁₋₂₀ alkyl, more preferably phenyl optionallysubstituted by C₁₋₆alkoxy (preferably methoxy) or unsubstitutedC₁₋₂₀alkyl (such as hexyl, octyl, decyl, dodecyl, tetradecyl, hexadecyl,stearyl).

A sulfinate group is preferably —OSOR₁₇ wherein R₁₇ can be hydrogen, analiphatic, heteroaliphatic, haloaliphatic, alicyclic, heteroalicyclic,aryl or heteroaryl group as defined above.

In certain embodiments, R₁₇ is unsubstituted aliphatic, alicyclic oraryl. Preferably R₁₇ is hydrogen, methyl, ethyl, propyl or phenyl.

A carbonate group is preferably OC(O)OR₁₈, wherein R₁₈ can be hydrogen,an aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl orheteroaryl group as defined above. In certain embodiments, R₁₈ isoptionally substituted aliphatic, alicyclic or aryl. Preferably R₁₈ ishydrogen, methyl, ethyl, propyl, butyl (for example n-butyl, isobutyl ortert-butyl), phenyl, pentafluorophenyl, pentyl, hexyl, heptyl, octyl,nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl,hexadecyl, heptadecyl, octadecyl, nonadecyl, eicosyl, trifluoromethyl,cyclohexyl, benzyl or adamantyl.

It will be appreciated that where any of the above groups are present ina Lewis base G, one or more additional R groups may be present, asappropriate, to complete the valency. For example, in the context of anamino group, an additional R group may be present to give RNHR₁₀,wherein R is hydrogen, an optionally substituted aliphatic,heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl group asdefined above. Preferably, R is hydrogen or aliphatic, alicyclic oraryl.

Any of the aliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, haloalkyl, alkoxy, aryloxy, alkylthio, arylthio, alkylaryl,silyl, silyl ether, ester, sulfoxide, sulfonyl, carboxylate, carbonate,imine, acetylide, amino, phosphinate, sulfonate or amido groups wherevermentioned in the definitions above, may optionally be substituted byhalogen, hydroxy, nitro, carboxylate, carbonate, alkoxy, aryloxy,alkylthio, arylthio, heteroaryloxy, alkylaryl, amino, amido, imine,nitrile, silyl, silyl ether, ester, sulfoxide, sulfonyl, acetylide,phosphinate, sulfonate or optionally substituted aliphatic,heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl groups(for example, optionally substituted by halogen, hydroxy, nitro,carbonate, alkoxy, aryloxy, alkylthio, arylthio, amino, imine, nitrile,silyl, sulfoxide, sulfonyl, phosphinate, sulfonate or acetylide).

It will be appreciated that although in formula (I), the groups X and Gare illustrated as being associated with a single M₁ or M₂ metal centre,one or more X and G groups may form a bridge between the M₁ and M₂ metalcentres.

For the purposes of the present invention, the epoxide substrate is notlimited. The term epoxide therefore relates to any compound comprisingan epoxide moiety. Examples of epoxides which may be used in the presentinvention include, but are not limited to, cyclohexene oxide, styreneoxide, propylene oxide, butylene oxide, substituted cyclohexene oxides(such as limonene oxide, C₁₀H₁₆O or2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, C₁₁H₂₂O), alkylene oxides(such as ethylene oxide and substituted ethylene oxides) or substitutedor unsubstituted oxiranes (such as oxirane, epichlorohydrin,2-(2-methoxyethoxy)methyl oxirane (MEMO),2-(2-(2-methoxyethoxy)ethoxy)methyl oxirane (ME2MO),2-(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)methyl oxirane (ME3MO),1,2-epoxybutane, glycidyl ethers), vinyl-cyclohexene oxide,3-phenyl-1,2-epoxypropane, 1,2- and 2,3-epoxybutane, isobutylene oxide,cyclopentene oxide, 2,3-epoxy-1,2,3,4-tetrahydronaphthalene, indeneoxide, and functionalized 3,5-dioxaepoxides. Examples of functionalized3,5-dioxaepoxides include:

The epoxide moiety may be a glycidyl ether, glycidyl ester or glycidylcarbonate. Examples of glycidyl ethers, glycidyl esters and glycidylcarbonates include:

The epoxide substrate may contain more than one epoxide moiety, i.e. itmay be a bis-epoxide, a tris-epoxide, or a multi-epoxide containingmoiety. Examples of compounds including more than one epoxide moietyinclude bisphenol A diglycidyl ether and 3,4-epoxycyclohexylmethyl3,4-epoxycyclohexanecarboxylate. It will be understood that reactionscarried out in the presence of one or more compounds having more thanone epoxide moiety may lead to cross-linking in the resulting polymer.

The skilled person will appreciate that the epoxide can be obtained from“green” or renewable resources. The epoxide may be obtained from a(poly)unsaturated compound, such as those deriving from a fatty acidand/or terpene, obtained using standard oxidation chemistries.

The epoxide moiety may contain —OH moieties, or protected —OH moieties.The —OH moieties may be protected by any suitable protecting group.Suitable protecting groups include methyl or other alkyl groups, benzyl,allyl, tert-butyl, tetrahydropyranyl (THP), methoxymethyl (MOM), acetyl(C(O)alkyl), benzolyl (C(O)Ph), dimethoxytrityl (DMT),methoxyethoxymethyl (MEM), p-methoxybenzyl (PMB), trityl, silyl (such astrimethylsilyl (TMS), t-Butyldimethylsilyl (TBDMS), t-Butyldiphenylsilyl(TBDPS), tri-iso-propylsilyloxymethyl (TOM), and triisopropylsilyl(TIPS)), (4-methoxyphenyl)diphenylmethyl (MMT), tetrahydrofuranyl (THF),and tetrahydropyranyl (THP).

The epoxide preferably has a purity of at least 98%, more preferably>99%.

It will be understood that the term “an epoxide” is intended toencompass one or more epoxides. In other words, the term “an epoxide”refers to a single epoxide, or a mixture of two or more differentepoxides. For example, the epoxide substrate may be a mixture ofethylene oxide and propylene oxide, a mixture of cyclohexene oxide andpropylene oxide, a mixture of ethylene oxide and cyclohexene oxide, or amixture of ethylene oxide, propylene oxide and cyclohexene oxide.

The skilled person will also understand that substituted andunsubstituted oxetanes can be used in place of, and in addition to, theepoxides of the second aspect of the invention. Suitable oxetanesinclude unsubstituted or substituted oxetanes (preferably substituted atthe 3-position by halogen, alkyl (unsubstituted or substituted by —OH orhalogen), amino, hydroxyl, aryl (e.g. phenyl), alkylaryl (e.g. benzyl)).Exemplary oxetanes include oxetane, 3-ethyl-3-oxetanemethanol,oxetane-3-methanol, 3-methyl-3-oxetanemethanol, 3-methyloxetane,3-ethyloxetane, etc.

The term anhydride relates to any compound comprising an anhydridemoiety in a ring system (i.e. a cyclic anhydride). Preferably, theanhydrides which are useful in the present invention have the followingformula:

Wherein m″ is 1, 2, 3, 4, 5, or 6 (preferably 1 or 2), each R^(a1),R^(a2), R^(a3) and R^(a4) is independently selected from hydrogen,halogen, hydroxyl, nitro, alkoxy, aryloxy, heteroaryloxy, amino,alkylamino, imine, nitrile, acetylide, carboxylate or optionallysubstituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic,aryl, heteroaryl, alkylaryl or alkylheteroaryl; or two or more ofR^(a1), R^(a2)R^(a3) and R^(a4) can be taken together to form asaturated, partially saturated or unsaturated 3 to 12 membered,optionally substituted ring system, optionally containing one or moreheteroatoms, or can be taken together to form a double bond. Each Q isindependently C, O, N or S, preferably C, wherein R^(a3) and R^(a4) areeither present, or absent, and

can either be

or

, according to the valency of Q. It will be appreciated that when Q isC, and

is

, R^(a3) and R^(a4) (or two R^(a4) on adjacent carbon atoms) are absent.The skilled person will appreciate that the anhydrides may be obtainedfrom “green” or renewable resources. Preferable anhydrides are set outbelow.

The term lactone relates to any cyclic compound comprising a-C(O)O—moiety in the ring. Preferably, the lactones which are useful in thepresent invention have the following formula:

Wherein m is 1 to 20 (e.g. 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,14, 15, 16, 17, 18, 19 or 20), preferably 2, 4, or 5; and R^(L1) andR^(L2) are independently selected from hydrogen, halogen, hydroxyl,nitro, alkoxy, aryloxy, heteroaryloxy, amino, alkylamino, imine,nitrile, acetylide, carboxylate or optionally substituted aliphatic,heteroaliphatic, alicyclic, heteroalicyclic, aryl, heteroaryl, alkylarylor alkylheteroaryl. Two or more of R^(L1) and R^(L2) can be takentogether to form a saturated, partially saturated or unsaturated 3 to 12membered, optionally substituted ring system, optionally containing oneor more heteroatoms. When m is 2 or more, the R^(L1) and R^(L2) on eachcarbon atom may be the same or different. Preferably R^(L1) and R^(L2)are selected from hydrogen or alkyl. Preferably, the lactone has thefollowing structure:

The term lactide is a cyclic compound containing two ester groups.Preferably, the lactides which are useful in the present invention havethe following formula:

Wherein m′ is 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10, (preferably 1 or 2, morepreferably, 1) and R^(L3) and R^(L4) are independently selected fromhydrogen, halogen, hydroxyl, nitro, alkoxy, aryloxy, heteroaryloxy,amino, alkylamino, imine, nitrile, acetylide, carboxylate or optionallysubstituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic,aryl, heteroaryl, alkylaryl or alkylheteroaryl. Two or more of R^(L3)and R^(L4) can be taken together to form a saturated, partiallysaturated or unsaturated 3 to 12 membered, optionally substituted ringsystem, optionally containing one or more heteroatoms, When m′ is 2 ormore, the R^(L3) and R^(L4) on each carbon atom may be the same ordifferent or one or more R^(L3) and R^(L4) on adjacent carbon atoms canbe absent, thereby forming a double or triple bond. It will beappreciated that while the compound has two moieties represented by(—CR^(L3)R^(L4))_(m′), both moieties will be identical. Preferably, m′is 1, R^(L4) is H, and R^(L3) is H, hydroxyl or a C₁₋₆alkyl, preferablymethyl. The stereochemistry of the moiety represented by(—CR^(L3)R^(L4))_(m′), can either be the same (for example RR-lactide orSS-lactide), or different (for example, meso-lactide). The lactide maybe a racemic mixture, or may be an optically pure isomer. Preferably,the lactide has the following formula:

The term “lactone and/or lactide” used herein encompasses a lactone, alactide and a combination of a lactone and a lactide. Preferably, theterm “lactone and/or lactide” means a lactone or a lactide.

Preferred optional substituents of the groups R^(a1), R, R², R^(a3),R^(a4), R^(L1), R^(L2), R^(L3) and R^(L4) include halogen, nitro,hydroxyl, unsubstituted aliphatic, unsubstituted heteroaliphaticunsubstituted aryl, unsubstituted heteroaryl, alkoxy, aryloxy,heteroaryloxy, amino, alkylamino, imine, nitrile, acetylide, andcarboxylate.

DETAILED DESCRIPTION

In the first aspect of the invention, there is provided a catalyst offormula (I):

wherein:M₁ and M₂ are independently selected from Zn(II), Cr(II), Co(II),Cu(II), Mn(II), Mg(II), Ni(II), Fe(II), Ti(II), V(II), Cr(III)-X,Co(III)-X, Ni(III)-X, Mn(III)-X, Fe(III)-X, Ca(II), Ge(II), AI(III)-X,Ti(III)-X, V(III)-X, Ge(IV)-(X)₂ or Ti(IV)-(X)₂;R₁ and R₂ are independently selected from hydrogen, halide, a nitrogroup, a nitrile group, an imine, an amine, an ether group, a silylgroup, a silyl ether group, a sulfoxide group, a sulfonyl group, asulfinate group or an acetylide group or an optionally substitutedalkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy,alkylthio, arylthio, alicyclic or heteroalicyclic group;R_(3A) and R_(3B) are independently selected from optionally substitutedalkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene,heteroalkynylene, arylene, heteroarylene or cycloalkylene, whereinalkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene andheteroalkynylene, may optionally be interrupted by aryl, heteroaryl,alicyclic or heteroalicyclic;R₅ is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl;E₁ is C, E₂ is O, S or NH or E₁ is N and E₂ is O;E₃, E₄, E₅ and E₆ are each independently selected from N, NR₄, O and S,wherein when any of E₃, E₄, E₅ or E₆ are N,

is

, and wherein when any of E₃, E₄, E₅ or E₆ are NR₄, O or S,

is

; R is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl;X is independently selected from OC(O)R^(x), OSO₂R^(x), OSOR^(x),OSO(R^(x))₂, S(O)R^(x), OR^(x), phosphinate, halide, nitrate, hydroxyl,carbonate, amino, amido or optionally substituted aliphatic,heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl;R_(x) is independently hydrogen, or optionally substituted aliphatic,haloaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,alkylaryl or heteroaryl; andG is absent or independently selected from a neutral or anionic donorligand which is a Lewis base;and wherein:

-   -   i) R_(3A) is different from R_(3B); and/or    -   ii) at least one occurrence of E₃, E₄, E₅ and E₆ is different to        a remaining occurrence of E₃, E₄, E₅ and E₆.

Preferably, each of the occurrences of the groups R₁ and R₂ may be thesame or different.

Preferably R, and R₂ are independently selected from hydrogen, halide,amino, nitro, sulfoxide, sulfonyl, sulfinate, silyl, silyl ether and anoptionally substituted alkyl, alkenyl, aryl, heteroaryl, alkoxy, aryloxyor alkylthio. Preferably each occurrence of R₂ is the same. Preferably,each occurrence of R₂ is the same, and is hydrogen.

Even more preferably, R₂ is hydrogen and R₁ is independently selectedfrom hydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate,silyl ether and optionally substituted alkyl, alkenyl, aryl, heteroaryl,alkoxy, aryloxy, alkylthio, arylthio, such as hydrogen, C₁₋₆alkyl (e.g.haloalkyl), alkoxy, aryl, halide, nitro, sulfonyl, silyl and alkylthio,for example, tertiary butyl, isopropyl, methyl, methyloxy, hydrogen,nitro, dimethylsulfoxide, trialkylsilyl for example triethylsilyl, silylether, halogen or phenyl. Most preferably R, is tertiary butyl and R₂ ishydrogen.

Each occurrence of R, can be the same or different, and R₁ and R₂ can bethe same or different. Preferably each occurrence of R, is the same.Preferably, each occurrence of R¹ is the same, and each occurrence of R₂is the same, and R, is different to R₂. The skilled person willappreciate that when each occurrence of R₁ is different, this adds tothe asymmetry of the catalyst.

It will be appreciated that the groups R_(3A) and R_(3B) can be adisubstituted alkyl, alkenyl, alkynyl, heteroalkyl, heteroalkenyl orheteroalkynyl group which may optionally be interrupted by an aryl,heteroaryl, alicyclic or heteroalicyclic group, or may be adisubstituted aryl or cycloalkyl group which acts as a bridging groupbetween two nitrogen centres in the catalyst of formula (I). Thus, whereR_(3A) or R₃₈ is an alkylene group, such as dimethylpropylene, theR_(3A) or R_(3B) group has the structure —CH₂—C(CH₃)₂—CH₂—. Thedefinitions of the alkyl, aryl, cycloalkyl etc groups set out abovetherefore also relate respectively to the alkylene, arylene,cycloalkylene etc groups set out for R_(3A) or R_(3B), and may beoptionally substituted. Exemplary options for R_(3A) and R_(3B) includeethylene, 2,2-dimethylpropylene, 2,2-fluoropropylene, propylene,butylene, phenylene, cyclohexylene or biphenylene, more preferably2,2-dimethylpropylene, 2,2-fluoropropylene, propylene, cyclohexylene orphenylene. When R_(3A) or R_(3B) is cyclohexylene, it can be theracemic, RR- or SS-forms. Preferably R_(3A) or R_(3B) are selected fromethylene, propylene, a substituted propylene, such as2,2-di(alkyl)propylene, phenylene, or cyclohexylene, more preferablyR_(3A) or R_(3B) are 2,2-di(methyl)propylene.

When each occurrence of E₃, E₄, E₅ and E₆ is the same, R_(3A) isdifferent to R_(3B). It will also be appreciated that when at least oneoccurrence of E₃, E₄, E₅ and E₆ is different to a remaining occurrenceof E₃, E₄, E₅ and E₆, R_(3A) can be the same as, or different to R_(3B).

Preferably, when R_(3A) is different to R_(3B), R_(3A) can be optionallysubstituted alkylene (for example, optionally substituted propylene,e.g. 2,2-dimethylpropylene, 2,2-fluoropropylene or propylene), oroptionally substituted cycloalkylene (such as cyclohexylene), and R_(3B)can be optionally substituted arylene (such as phenylene orbiphenylene), or optionally substituted alkylene (for example,optionally substituted propylene, e.g. 2,2-dimethylpropylene,2,2-fluoropropylene, ethylene or propylene).

In a first preferred embodiment, R_(3A) is 2,2-dimethylpropylene, andR_(3B) is phenylene.

In a second preferred embodiment, R_(3A) is a disubstitutedcycloalkylene which acts as a bridging group between two nitrogencentres in the catalyst of formula (I), and R_(3B) is2,2-dimethylpropylene.

In a third preferred embodiment, R_(3A) is 2,2-dimethylpropylene, andR_(3B) is propylene or ethylene.

In a fourth preferred embodiment, R_(3A) is propylene, and R_(3B) is2,2-dimethylpropylene.

E₃, E₄, E₅ and E₆ are each independently selected from N, NR₄, O or S.The skilled person will understand that when any of E₃, E₄, E₅ or E₆ areN,

is

. It will also be understood that when any of E₃, E₄, E₅ or E₆ are NR₄,O or S,

is

.

When R_(3A) and R_(3B) are the same, at least one occurrence of E₃, E₄,E₅ or E₆ is different to a remaining occurrence of E₃, E₄, E₅ and E₆.

Preferably when at least one occurrence of E₃, E₄, E₅ or E₆ is differentto a remaining occurrence of E₃, E₄, E₅ and E₆, each E₃, E₄, E₅ and E₆is NR₄, but at least one of the R₄ groups is different from a remainingR₄ groups.

Alternatively, when at least one occurrence of E₃, E₄, E₅ or E₆ isdifferent to a remaining occurrence of E₃, E₄, E₅ and E₆, and at leastone occurrence of E₃, E₄, E₅ or E₆ is NR₄, at least one of the remainingE₃, E₄, E₅ and E₆ groups is selected from N, O or S.

It will be understood that when R_(3A) is different to R_(3B), each E₃,E₄, E₅ and E₆ may be the same or different.

Preferably, when R_(3A) is different to R_(3B), each E₃, E₄, E₅ and E₆are the same. When each of E₃, E₄, E₅ and E₆ are the same, preferablyeach of E₃, E₄, E₅ and E₆ are NR₄, more preferably each of E₃, E₄, E₅and E₆ are NH.

It will be understood that E₃ and E₅ may be the same, E₃ and E₄ may bethe same, E₄ and E₆ may be the same, E₄ and E₅ may be the same, E₅ andE₆ may be the same, and/or E₃ and E₆ may be the same. It is preferredthat E₃ and E₅ are the same, and E₄ and E₆ are the same, and E₃ and E₅are different to E₄ and E₆, preferably E₃ and E₅ are S or O and E₄ andE₆ are N or NR₄ (such as NH). Alternatively, E₃ and E₄ can be the same,and E₅ and E₆ can be the same, and E₃ and E₄ are different to E₅ and E₆,preferably E₃ and E₄ are S and E₅ and E₆ are N or NR₄ (such as NH).

Preferably each R₄ is independently selected from hydrogen, and anoptionally substituted alkyl, alkenyl, alkynyl, aryl, heteroalkyl,heteroalkenyl, heteroalkynyl or heteroaryl. Preferably, at least one R₄is hydrogen. At least one R₄ is may be different to a remaining R₄group/s. When each R₄ is the same, it is preferably selected fromhydrogen, and an optionally substituted alkyl, alkenyl, alkynyl, aryl,heteroalkyl, heteroalkenyl, heteroalkynyl or heteroaryl. Exemplaryoptions for R₄ include hydrogen, methyl, ethyl, n-propyl, n-butyl,isopropyl, tertiary butyl, benzyl, phenyl, -alkyl-C(O)—OR₁₉ (as definedhereinabove for example methyl propanoate), alkyl nitrile of the formula-alkyl-C≡N or alkyl ketone/aldehyde of the formula alkyl-C(O)—R₁₉. Afurther exemplary option is methylpyridine.

Preferably each E₃, E₄, E₅ and E₆ is NR₄, and one of the R₄ groups isdifferent, preferably E₄ is different. More preferably one of the R₄groups is selected from an optionally substituted alkyl or heteroalkyl.Still more preferably one of the R₄ groups is selected from methyl,ethyl, propyl, butyl or -alkyl-C(O)—OR₁₉ as defined hereinabove, forexample methyl propanoate. Preferably the remaining R₄ groups arehydrogen.

Preferably each E₃, E₄, E₅ and E₆ is NR₄, and two of the R₄ groups aredifferent, preferably E₃ and E₅ are different or E₄ and E₅ aredifferent. More preferably two of the R₄ groups are selected from anoptionally substituted alkyl or heteroalkyl. Still more preferably twoof the R₄ groups are selected from methyl, ethyl, propyl, butyl or-alkyl-C(O)—OR₁₉ as defined hereinabove, for example methyl propanoate.Preferably the remaining R₄ groups are hydrogen.

Preferably two of E₃, E₄, E₅ and E₆ are NR₄, and two of E₃, E₄, E₅ andE₆ are N. More preferably two of E₃, E₄, E₅ and E₆ are NH and two of E₃,E₄, E₅ and E₆ are N. Still more preferably, E₄ and E₆ are NH and E₃ andE₅ are N, or E₃ and E₅ are NH and E₄ and E₆ are N.

Preferably two of E₃, E₄, E₅ and E₆ are S, and two of E₃, E₄, E₅ and E₆are NR₄. More preferably two of E₃, E₄, E₅ and E₆ are S, and two of E₃,E₄, E₅ and E₆ are NH. Still more preferably E₃ and E₅ are S, and, E₄ andE₆ are NH.

Preferably each R₅ is independently selected from hydrogen, andoptionally substituted aliphatic or aryl. More preferably, each R₅ isindependently selected from hydrogen, and optionally substituted alkylor aryl. Even more preferably, each R₅ is the same, and is selected fromhydrogen, and optionally substituted alkyl or aryl. Exemplary R₅ groupsinclude hydrogen, methyl, ethyl, phenyl and trifluoromethyl, preferablyhydrogen, methyl or trifluoromethyl. Even more preferably, each R₅ ishydrogen.

Preferably both occurrences of E₁ are C and both occurrences of E₂ arethe same, and selected from O, S or NH. Even more preferably, bothoccurrences of E, are C and both occurrences of E₂ are O.

Each X is independently selected from OC(O)R^(x), OSO₂R^(x), OS(O)R^(x),OSO(R^(x))₂, S(O)R^(x), OR^(x), phosphinate, halide, nitro, hydroxyl,carbonate, amino, amido and optionally substituted aliphatic,heteroaliphatic (for example silyl), alicyclic, heteroalicyclic, aryl orheteroaryl. Preferably each X is independently OC(O)R^(x), OSO₂R^(x),OS(O)R^(x), OSO(R^(x))₂, S(O)R^(x), OR^(x), halide, nitrate, hydroxyl,carbonate, amino, nitro, amido, alkyl (e.g. branched alkyl),heteroalkyl, (for example silyl), aryl or heteroaryl. In particularlypreferred embodiments, each X is independently OC(O)R^(x), OR^(x),halide, carbonate, amino, nitro, alkyl, aryl, heteroaryl, phosphinate orOSO₂R^(x). Preferred optional substituents for when X is aliphatic,heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl includehalogen, hydroxyl, nitro, cyano, amino, or substituted or unsubstitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl orheteroaryl. Each X may be the same or different and preferably each X isthe same.

R^(x) is independently hydrogen, or optionally substituted aliphatic,haloaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,alkylaryl or heteroaryl. Preferably, R^(x) is alkyl, alkenyl, alkynyl,heteroalkyl, aryl, heteroaryl or alkylaryl. Preferred optionalsubstitutents for R^(x) include halogen, hydroxyl, cyano, nitro, amino,alkoxy, alkylthio, or substituted or unsubstituted aliphatic,heteroaliphatic, alicyclic, heteroalicyclic, aryl or heteroaryl (e.g.optionally substituted alkyl, aryl, or heteroaryl).

Exemplary options for X include acetate, trifluoroacetyl, octanoate,carbonate, 2-ethylhexanoate, cyclohexylbutyrate, dimethyl sulfonyl,ethyl, methyl, methyloxy, isopropyloxy, tertiary butyloxy, halogen (suchas chloride, bromide, iodide, fluoride), diisopropylamide orbis(trimethylsilyl)amide phenoxy, n-butyloxy, salicylate, dioctylphosphinate, diphenyl phosphinate etc. Preferably X is acetate.

M₁ and M₂ are independently selected from Zn(II), Cr(III), Cr(II),Co(III), Co(II), Cu(II), Ni(II), Ni(III), Mn(III), Mn(II), Mg(II),Fe(II), Fe(III), Ca(II), Ge(II), Ti(II), AI(III), Ti(III), V(II),V(III), Ge(IV) or Ti(IV). Preferably, M₁ and M₂ are independentlyselected from Zn(II), Cr(III), Co(II), Mn(II), Mg(II), Ni(II), Ni(III),Fe(II) and Fe(III), even more preferably, M₁ and M₂ are independentlyselected from Zn(II), Cr(III), Co(II), Mn(II), Ni(II), Ni(III), Mg(II),Fe(II), and Fe(III), and even more preferably, M₁ and M₂ areindependently selected from Zn(II), Ni(II), Ni(III) and Mg(II). Stillmore preferably M₁ and M₂ are independently selected from Ni(II),Ni(III), or Mg(II). Preferably M₁ and M₂ are the same. Most preferablyM₁ and M₂ are the same and are Ni(II) or Mg(II).

It will be appreciated that when M₁ or M₂ is Cr(III), Co(III), Mn(III),Ni(III) or Fe(III), the catalyst of formula (I) will contain anadditional X group co-ordinated to the metal centre, wherein X is asdefined above. It will also be appreciated that when M₁ or M₂ is Ge(IV)or Ti(IV), the catalyst of formula (III) will contain two additional Xgroup co-ordinated to the metal centre, wherein X is as defined above.It will be understood that when M₁ or M₂ is Ge(IV) or Ti(IV), both G maybe absent.

When G is not absent, it is a group which is capable of donating a lonepair of electrons (i.e. a Lewis base). G can be a nitrogen-containingLewis base. Each G may be neutral or negatively charged. If G isnegatively charged, then one or more positive counterions will berequired to balance out the charge of the complex. Suitable positivecounterions include group 1 metal ions (Na⁺, K⁺, etc), group 2 metalions (Mg²⁺, Ca²⁺, etc), imidazolium ions, a positively chargedoptionally substituted heteroaryl, heteroaliphatic or heteroalicyclicgroup, ammonium ions (i.e. N(R¹²)₄ ⁺), iminium ions (i.e.(R¹²)₂C═N(R¹²)₂ ⁺, such as bis(triphenylphosphine)iminium ions) orphosphonium ions (P(R¹²)₄ ⁺), wherein each R¹² is independently selectedfrom hydrogen or optionally substituted aliphatic, heteroaliphatic,alicyclic, heteroalicyclic, aryl or heteroaryl. Exemplary counterionsinclude [H-B]⁺ wherein B is selected from triethylamine,1,8-diazabicyclo[5.4.0]undec-7-ene and7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene.

G is preferably independently selected from an optionally substitutedheteroaliphatic group, an optionally substituted heteroalicyclic group,an optionally substituted heteroaryl group, a halide, hydroxide,hydride, a carboxylate and water. More preferably, G is independentlyselected from water, an alcohol (e.g methanol), a substituted orunsubstituted heteroaryl (imidazole, methyl imidazole (for example,N-methyl imidazole), pyridine, 4-dimethylaminopyridine, pyrrole,pyrazole, etc), an ether (dimethyl ether, diethylether, cyclic ethers,etc), a thioether, carbene, a phosphine, a phosphine oxide, asubstituted or unsubstituted heteroalicyclic (morpholine, piperidine,tetrahydrofuran, tetrahydrothiophene, etc), an amine, an alkyl aminetrimethylamine, triethylamine, etc), acetonitrile, an ester (ethylacetate, etc), an acetamide (dimethylacetamide, etc), a sulfoxide(dimethylsulfoxide, etc), a carboxylate, a hydroxide, hydride, a halide,a nitrate, a sulfonate, etc. It will be appreciated that one or bothinstances of G can be independently selected from optionally substitutedheteroaryl, optionally substituted heteroaliphatic, optionallysubstituted heteroalicyclic, halide, hydroxide, hydride, an ether, athioether, carbene, a phosphine, a phosphine oxide, an amine, an alkylamine, acetonitrile, an ester, an acetamide, a sulfoxide, a carboxylate,a nitrate or a sulfonate. G may be a halide; hydroxide; hydride; water;a heteroaryl, heteroalicyclic or carboxylate group which are optionallysubstituted by alkyl, alkenyl, alkynyl, alkoxy, halogen, hydroxyl, nitroor nitrile. Preferably, G is independently selected from halide; water;a heteroaryl optionally substituted by alkyl (e.g. methyl, ethyl etc),alkenyl, alkynyl, alkoxy (preferably methoxy), halogen, hydroxyl, nitroor nitrile. It will be understood that one or both instances of G may benegatively charged (for example, halide). Preferably, one or bothinstances of G is an optionally substituted heteroaryl. Exemplary Ggroups include chloride, bromide, pyridine, methylimidazole (for exampleN-methyl imidazole) and dimethylaminopyridine (for example,4-methylaminopyridine).

It will be appreciated that when a G group is present, the G group maybe associated with a single M metal centre as shown in formula (I), orthe G group may be associated with both metal centres and form a bridgebetween the two metal centres, as shown below in formula (Ia):

Wherein R₁, R₂, R_(3A), R_(3B), R₄, E₁, E₂, E₃, E₄, E₅, E₆, R₅, M, G andX, are as defined for formula (I). It will also be appreciated that Xmay form a bridge between the two metal centres.

The skilled person will understand that, in the solid state, thecatalysts of the first aspect may be associated with solvent moleculessuch as water, or alcohol (e.g. methanol or ethanol). It will beappreciated that the solvent molecules may be present in a ratio of lessthan 1:1 relative to the molecules of catalyst of the first aspect (i.e.0.2:1, 0.25:1, 0.5:1), in a ratio of 1:1, relative to the molecules ofcatalyst of the first aspect, or in a ratio of greater than 1:1,relative to the molecules of catalyst of the first aspect.

The skilled person will understand that, in the solid state, thecatalysts of the first aspect may form aggregates. For example, thecatalyst of the first aspect may be a dimer, a trimer, a tetramer, apentamer, or higher aggregate.

It will be appreciated that the preferred features described above forthe catalyst of the first aspect may be present in combination mutatismutandis.

For example, each occurrence of R₂ and R₅ are H, E, is C and E₂ is O, Sor NH (preferably E₂ is O).

Preferably, both occurrences of R, are the same, and are selected fromhydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate, silyl,silyl ether and an optionally substituted alkyl, alkenyl, aryl,heteroaryl, alkoxy, aryloxy or alkylthio; R₂ is hydrogen; R_(3A) andR_(3B) are the same or different, and are selected from substituted orunsubstituted alkylene, substituted or unsubstituted cycloalkylene andsubstituted or unsubstituted arylene; E₃ to E₆ are the same or differentand are selected from NR₄, S, N or O; R₄ is hydrogen, an optionallysubstituted alkyl or heteroalkyl; each X is the same, and is selectedfrom OC(O)R^(x), OR^(x), halide, carbonate, amino, nitro, alkyl, aryl,heteroaryl, phosphinate or OSO₂R^(x), R^(x) is alkyl, alkenyl, alkynyl,heteroalkyl, aryl, heteroaryl or alkylaryl; R^(x) is alkyl, alkenyl,alkynyl, heteroalkyl, aryl, heteroaryl or alkylaryl; each G (wherepresent) is independently selected from halide; water; a heteroaryloptionally substituted by alkyl, alkenyl, alkynyl, alkoxy, halogen,hydroxyl, nitro or nitrile; M₁ and M₂ are independently selected fromMg(II), Zn(II), Cr(II), Cr(III)-X, Co(II), Co(III)-X, Mn(II), Ni(II),Ni(III)-X, Fe(II), and Fe(III)-X, preferably M₁ and M₂ are independentlyselected from Mg(II), Ni(II), Ni(III)-X and Zn(II). Preferably M, and M₂are the same, and are selected from Ni(II) or Mg(II).

Preferably, both occurrences of R, are the same, and are selected fromhydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate, silyl,silyl ether and an optionally substituted alkyl, alkenyl, aryl,heteroaryl, alkoxy, aryloxy or alkylthio; R₂ is hydrogen; R_(3A) is asubstituted or unsubstituted cycloalkylene or alkylene and R_(3B) is asubstituted or unsubstituted alkylene or arylene; each occurrence of E₃to E₆ is NR₄; R₄ is hydrogen; each X is the same, and is selected fromOC(O)R^(x), OR^(x), halide, carbonate, amino, nitro, alkyl, aryl,heteroaryl, phosphinate or OSO₂R^(x), R^(x) is alkyl, alkenyl, alkynyl,heteroalkyl, aryl, heteroaryl or alkylaryl; R^(x) is alkyl, alkenyl,alkynyl, heteroalkyl, aryl, heteroaryl or alkylaryl; each G (wherepresent) is independently selected from halide; water; a heteroaryloptionally substituted by alkyl, alkenyl, alkynyl, alkoxy, halogen,hydroxyl, nitro or nitrile; M₁ and M₂ are independently selected fromMg(II), Zn(II), Cr(II), Cr(III)-X, Co(II), Co(III)-X, Mn(II), Ni(II),Ni(III)-X, Fe(II), and Fe(III)-X, preferably M₁ and M₂ are independentlyselected from Mg(II), Ni(II), Ni(III)-X and Zn(II). Still morepreferably M₁ and M₂ are independently selected from Ni(II), Ni(III), orMg(II). Preferably M₁ and M₂ are the same, and are selected from Ni(II)or Mg(II).

Preferably, both occurrences of R, are the same, and are selected fromhydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate, silyl,silyl ether and an optionally substituted alkyl, alkenyl, aryl,heteroaryl, alkoxy, aryloxy or alkylthio; R₂ is hydrogen; R_(3A) andR_(3B) are the same and are substituted or unsubstituted alkylene; eachof E₃, E₄, E₅ and E₆ is NR₄ wherein one of the R₄ groups is differentfrom a remaining R₄ group and is selected from an optionally substitutedalkyl or heteroalkyl and the remaining R₄ group/s are hydrogen; each Xis the same, and is selected from OC(O)R^(x), OR^(x), halide, carbonate,amino, nitro, alkyl, aryl, heteroaryl, phosphinate or OSO₂R^(x), R^(x)is alkyl, alkenyl, alkynyl, heteroalkyl, aryl, heteroaryl or alkylaryl;R^(x) is alkyl, alkenyl, alkynyl, heteroalkyl, aryl, heteroaryl oralkylaryl; each G (where present) is independently selected from halide;water; a heteroaryl optionally substituted by alkyl, alkenyl, alkynyl,alkoxy, halogen, hydroxyl, nitro or nitrile; M₁ and M₂ are independentlyselected from Mg(II), Zn(II), Cr(II), Cr(III)-X, Co(II), Co(III)-X,Mn(II), Ni(II), Ni(III)-X, Fe(II), and Fe(III)-X, preferably M₁ and M₂are independently selected from Mg(II), Ni(II), Ni(III)-X and Zn(II).Still more preferably M₁ and M₂ are independently selected from Ni(II),Ni(III), or Mg(II). Preferably M₁ and M₂ are the same, and are selectedfrom Ni(II) or Mg(II).

Preferably both occurrences of R, are the same, and are selected fromhydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate, silyl,silyl ether and an optionally substituted alkyl, alkenyl, aryl,heteroaryl, alkoxy, aryloxy or alkylthio; R₂ is hydrogen; R_(3A) andR_(3B) are selected from substituted or unsubstituted alkylene,substituted or unsubstituted cycloalkylene and substituted orunsubstituted arylene; E₃ to E₆ are selected from N, NR₄, S or O; R₄ isselected from hydrogen, or optionally substituted alkyl or heteroalkyl;each X is the same, and is selected from OC(O)R^(x), OR^(x), orOSO₂R^(x), R^(x) is alkyl, alkenyl, alkynyl, heteroalkyl, aryl,heteroaryl or alkylaryl; each G (where present) is independentlyselected from halide; water; a heteroaryl optionally substituted byalkyl, alkenyl, alkynyl, alkoxy, halogen, hydroxyl, nitro or nitrile; M₁and M₂ are independently selected from Mg(II), Zn(II), Cr(II),Cr(III)-X, Co(II), Co(III)-X, Mn(II), Ni(II), Ni(III)-X, Fe(II), andFe(III)-X, preferably M₁ and M₂ are independently selected from Mg(II),Ni(II), Ni(III)-X and Zn(II). Still more preferably M₁ and M₂ areindependently selected from Ni(II), Ni(III), or Mg(II). Preferably M₁and M₂ are the same, and are selected from Ni(II) or Mg(II); wherein:

-   -   i) R_(3A) is different from R_(3B); and/or    -   ii) at least one occurrence of E₃, E₄, E₅ and E₆ is different to        a remaining occurrence of E₃, E₄, E₅ and E₆.

More preferably, both occurrences of R, are the same, and are selectedfrom an optionally substituted alkyl; R₂ is hydrogen; R_(3A) and R_(3B)are selected from substituted or unsubstituted alkylene, substituted orunsubstituted cycloalkylene, and substituted or unsubstituted arylene;each occurrence of E₃ to E₆ is NR₄; R₄ is selected from hydrogen, oroptionally substituted alkyl or heteroalkyl; each X is the same, and isselected from OC(O)R^(x), OR^(x), or OSO₂R^(x), R^(x) is alkyl, alkenyl,alkynyl, heteroalkyl, aryl, heteroaryl or alkylaryl; M₁ and M₂ areindependently selected from Mg(II), Ni(II), Ni(III)-X and Zn(II). Stillmore preferably M₁ and M₂ are independently selected from Ni(II),Ni(III), or Mg(II). Preferably M₁ and M₂ are the same, and are selectedfrom Ni(II) or Mg(II); wherein:

-   -   i) R_(3A) is different from R₃₈; and/or    -   ii) at least one occurrence of E₃, E₄, E₅ and E₆ is different to        a remaining occurrence of E₃, E₄, E₅ and E₆.

Still more preferably, both occurrences of R, are the same, and aretertiary butyl; R₂ is hydrogen; R_(3A) and R_(3B) are selected frombutylene, benzylene, ethylene, propylene, 2,2-dimethylpropylene; eachoccurrence of E₃ to E₆ is NR₄; R₄ is selected from hydrogen, methyl,ethyl, propyl, butyl, or -alkyl-C(O)—OR₁₉ as defined hereinabove,preferably methyl propanoate; each X is the same, and is OAc; M₁ and M₂are independently selected from Mg(II), Ni(II), Ni(III)-X and Zn(II).Still more preferably M₁ and M₂ are independently selected from Ni(II),Ni(III), or Mg(II). Preferably M₁ and M₂ are the same, and are selectedfrom Ni(II) or Mg(II); wherein:

-   -   i) R_(3A) is different from R_(3B); and/or    -   ii) at least one occurrence of E₃, E₄, E₅ and E₆ is different to        a remaining occurrence of E₃, E₄, E₅ and Ee.

Exemplary catalysts of the first aspect are as follows:

More preferably the catalyst of formula (I) is:

In the second aspect of the invention, there is provided a ligand offormula (II):

wherein:R₁ and R₂ are independently selected from hydrogen, halide, a nitrogroup, a nitrile group, an imine, an amine, an ether group, a silylgroup, a silyl ether group, a sulfoxide group, a sulfonyl group, asulfinate group or an acetylide group or an optionally substitutedalkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy,alkylthio, arylthio, alicyclic or heteroalicyclic group;R_(3A) and R_(3B) are independently selected from optionally substitutedalkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene,heteroalkynylene, arylene, heteroarylene or cycloalkylene, whereinalkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene andheteroalkynylene, may optionally be interrupted by aryl, heteroaryl,alicyclic or heteroalicyclic;R₅ is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl; E, is C, E₂ is OY, S or NH orE₁ is N and E₂ is O;Y is hydrogen or an alkali metal;E₃, E₄, E₅ and E₆ are each independently selected from N, NR₄, O and S,wherein when any of E₃, E₄, E₅ or E₆ are N,

is

, and wherein when any of E₃, E₄, E₅ or E₆ are NR₄, O or S,

is

; R₄ is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl;and wherein:

-   -   i) R_(3A) is different from R_(3B); and/or    -   ii) at least one occurrence of E₃, E₄, E₅ and E₆ is different to        a remaining occurrence of E₃, E₄, E₅ and E₆.

All of the preferred features defined hereinabove in relation to thefirst aspect apply in relation to the second aspect. In particular, allof the preferred features in relation to the groups R₁, R₂, R_(3A),R_(3B), R₄, R₅, E₁, E₂, E₃, E₄, E₅, and E₆ apply equally to the secondaspect.

Preferably Y is selected from hydrogen, lithium, sodium, potassium,rubidium, caesium, or francium. More preferably Y is either hydrogen orlithium.

Preferably both occurrences of R₁ are the same, and are selected fromhydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate, silyl,silyl ether and an optionally substituted alkyl, alkenyl, aryl,heteroaryl, alkoxy, aryloxy or alkylthio; R₂ is hydrogen; R_(3A) andR_(3B) are selected from substituted or unsubstituted alkylene,substituted or unsubstituted cycloalkylene and substituted orunsubstituted arylene; E₃ to E₆ are N, NR₄, S or O; R₄ is selected fromhydrogen, or optionally substituted alkyl or heteroalkyl;

wherein:

-   -   iii) R_(3A) is different from R_(3B); and/or    -   iv) at least one occurrence of E₃, E₄, E₅ and E₆ is different to        a remaining occurrence of E₃, E₄, E₅ and E₆.

More preferably, both occurrences of R, are the same, and are selectedfrom an optionally substituted alkyl; R₂ is hydrogen; R_(3A) and R_(3B)are selected from substituted or unsubstituted alkylene, substituted orunsubstituted cycloalkylene, and substituted or unsubstituted arylene;each occurrence of E₃ to E₆ is NR₄; R₄ is selected from hydrogen, oroptionally substituted alkyl or heteroalkyl;

-   -   wherein:    -   i) R_(3A) is different from R_(3B); and/or    -   ii) at least one occurrence of E₃, E₄, E₅ and E₆ is different to        a remaining occurrence of E₃, E₄, E₅ and E₆.

Still more preferably, both occurrences of R₁ are the same and aretertiary butyl; R₂ is hydrogen; R_(3A) and R_(3B) are selected fromtertiary butylene, benzylene, ethylene, propylene,2,2-dimethylpropylene; each occurrence of E₃ to E₆ is NR₄; R₄ isselected from hydrogen, methyl, ethyl, propyl, butyl, or-alkyl-C(O)—OR₁₉ as defined hereinabove, preferably methyl propanoate;

-   -   wherein:    -   i) R_(3A) is different from R_(3B); and/or    -   ii) at least one occurrence of E₃, E₄, E₅ and E₆ is different to        a remaining occurrence of E₃, E₄, E₅ and E₆.

More preferably still, the ligand of formula (II) is:

wherein:R₁ is tertiary butyl; R₂ is hydrogen; R₃ is 2,2-dimethylpropylene; andR₄ is selected from methyl, ethyl, propyl, or butyl;or the ligand of formula (II) is:

or the ligand of formula (II) is:

or the ligand of formula (II) is:

or the ligand of formula (II) is:

wherein:R₃ is selected from 2,2-dimethylpropylene, propylene, or ethylene;or the ligand of formula (II) is:

or the ligand of formula (II) is:

or the ligand of formula (II) is:

wherein:R is methyl or hydrogen;or the ligand of formula (II) is:

or the ligand of formula (II) is:

wherein:R₁ is tertiary butyl; R₂ is hydrogen; R₃ is 2,2-dimethylpropylene; andR₄ is methyl, ethyl, propyl, or butyl. Preferably R₄ is methyl.

More preferably still, the ligand of formula (II) comprises at least oneN-substituent, and may be selected from:

wherein:R₁ is tertiary butyl; R₂ is hydrogen; R₃ is 2,2-dimethylpropylene; andR₄ is selected from methyl, ethyl, propyl, or butyl;or:

Wherein

R₁ is tertiary butyl; R₂ is hydrogen; R₃ is 2,2-dimethylpropylene; andR₄ is methyl, ethyl, propyl, or butyl. Preferably R₄ is methyl.

In the third aspect, the invention extends to methods of preparation ofligands, complexes and catalysts according to the second aspect andfirst aspect respectively or as otherwise defined herein.

In the fourth aspect of the present invention, there is provided aprocess of asymmetric N-substitution of a symmetrical ligand having atetraaminophenol coordination sphere, the process comprising thefollowing steps:

-   -   a) protecting at least two of the amino groups of the        coordination sphere of the symmetrical ligand with an optionally        substituted alkylene;    -   b) asymmetrically N-substituting one or more of the protected        amino groups of the product of step (a) with a substituent.

Preferably the symmetrical ligand comprises formula (IV):

wherein:R, and R₂ are as defined above in relation to the second aspect, and R₃is defined as R_(3A) or R_(3B) in relation to the second aspect.

More preferably therefore, the symmetrical ligand of formula (IVa) is:

Preferably the optionally substituted alkylene is selected from anoptionally substituted methylene or ethylene.

Preferably the optionally substituted alkylene is derived from aprotecting reagent. Preferably therefore step (a) comprises reacting thesymmetrical ligand with a protecting reagent comprising an optionallysubstituted alkyl group. Preferably the protecting reagent is analdehyde, more preferably an aldehyde selected from formaldehyde orbenzaldehyde.

Preferably step (a) comprises protecting two or more of the amino groupsof the coordination sphere of the symmetrical ligand by forming bridginggroups between the adjacent amino or phenolic groups. Preferably thebridging groups are the optionally substituted alkylene, and areselected from an optionally substituted methylene or ethylene.

Preferably the product of step (a) comprises a pair of optionallysubstituted alkylene bridges between adjacent nitrogen atoms of thecoordination sphere.

Preferably step (a) is conducted in the presence of a solvent which maybe any suitable solvent for the protecting reagent, for example methanolor THF.

Preferably step (a) comprises contact with the protecting reagent forsufficient time to complete or substantially complete the reaction.Suitable contact times are between 30 minutes and 15 hours, morepreferably for between 2 hours and 8 hours, most preferably for around 6hours.

Preferably step (a) is conducted at a suitable temperature. Suitabletemperatures may be in the range −25 to 75° C., for example 0 to 50° C.,typically 15-30° C. such as room temperature (around 21° C.).

Preferably step (b) comprises asymmetrically N-substituting one or moreof the protected amino groups of the product of step (a) with anN-substituting agent by for example hydroamination with an alkene (suchas an acrylate or acrylonitrile) or by using an alkylating agent.

Preferably the substituent is an R₄ group, as defined hereinabove.Preferably therefore, one or more of the amino groups is substituted toform an NR₄ group.

Preferably step (b) comprises asymmetrically N-substituting one or moreof the protected amino groups of the product of step (a) with asubstituent. More preferably step (b) comprises asymmetricallyN-substituting one or more of the protected amino groups of the productof step (a) with a substituent by reacting the product of step (a) withan N-substituting agent.

Preferably the N-substituting agent is an alkylating agent or an alkenesuch as an activated alkene for example an alkyl acrylate, alkylmethacrylate, alkyl vinyl ketone or acrylonitrile, more preferably thealkylating agent comprises the formula R₄X. Preferably X is a halide,tosylate or triflate, more preferably X is iodine. In one preferredembodiment, R₄X is selected from iodomethane, iodoethane, 1-iodopropaneor 1-iodobutane.

Preferably step (b) is conducted in the presence of a solvent which maybe any suitable solvent for N-substituting agent, for example methanol,dichloromethane, or THF.

Preferably step (b) comprises contact with the N-substituting agent forsufficient time to complete or substantially complete the reaction.Suitable contact times are between 12 and 22 hours, more preferablybetween 14 and 18 hours, most preferably for around 16 hours.

Preferably step (b) is conducted at a suitable temperature. Suitabletemperatures may be between 20° C. to 90° C., more preferably between23° C. to 80° C., most preferably at around 25-50° C.

The method may further comprise step (c) hydrolysing the optionallysubstituted alkylene bridging groups between the adjacent amino groups.

Preferably the hydrolysing of step (c) is performed by reacting theproduct of step (b) with an acid, more preferably with HCl andsubsequently isolating the material Optionally, the method may furthercomprise upstream steps of formation of the symmetrical ligand having atetraaminophenol coordination sphere.

Preferably the method further comprises upstream steps of formation ofthe symmetrical ligand comprising formula (IV):

wherein:R₁ and R₂ are as defined above in relation to the second aspect, and R₃is defined as R_(3A) or R_(3B) in relation to the second aspect.

More preferably therefore, the method further comprises upstream stepsof formation of the symmetrical ligand comprising formula (IVa):

Preferably the upstream steps comprise (1) formation of a symmetricalligand having a tetraiminophenol coordination sphere, and (2) reductionof the imine groups to amine groups.

Preferably upstream step (1) comprises formation of a symmetrical ligandhaving a tetraiminophenol coordination sphere from a compound of formula(III):

wherein R₁ and R₂ are as defined hereinabove.

More preferably upstream step (1) comprises reacting a compound offormula (III) with an amine of formula H₂N—R₃—NH₂, wherein R₃ is asdefined hereinabove.

Upstream step (1) may be conducted in the presence of a suitablesolvent, an acid and an electrolyte.

The solvent may be any suitable solvent for the reactants of upstreamstep (1), for example methanol or THF. More preferably the solvent ismethanol.

Preferably upstream step (2) comprises reacting the product of upstreamstep (1) with a reducing agent.

Suitable reducing agents are known to those skilled in the art, forexample sodium borohydride or hydrogen.

Preferably upstream step (2) is conducted in the presence of a solvent,which may be any suitable solvent for the reactants of upstream step(2), for example methanol or THF. More preferably the solvent ismethanol.

In one preferred embodiment, the process comprises the following steps:

-   -   (a) forming a symmetrical ligand having a tetraiminophenol        coordination sphere;    -   (b) reducing the imino groups of the product of step (a) to        amino groups;    -   (c) protecting the amino groups of the product of step (b) with        an optionally substituted alkylene;    -   (d) asymmetrically N-substituting one or more of the protected        amino groups of the product of step (c) with a substituent;    -   (e) hydrolysing the optionally substituted alkylene groups of        the product of step (d) to remove the alkylene bridging group;    -   (f) optional neutralisation of the product of step (e).

In a more preferred embodiment, the process comprises the followingsteps:

-   -   (a) reacting a compound of formula (III) with an amine of        formula H₂N—R₃—NH₂ to form a ligand having a tetraiminophenol        coordination sphere;

-   -   (b) reducing the imino groups of the product of step (a) to        amino groups;    -   (c) protecting the amino groups of the product of step (b) by        forming bridging groups between the adjacent amino groups,        wherein the bridging groups are optionally substituted        alkylenes;    -   (d) asymmetrically N-substituting one or more of the protected        amino groups of the product of step (c) with an N-substituting        agent;    -   (e) hydrolysing the optionally substituted alkylene groups of        the product of step (d);    -   (f) optional neutralisation of the product of step (e);    -   wherein R₁, R₂, R₃, R₄ and X are as defined in relation to the        second aspect.

Preferably the asymmetrical ligand produced is that according to thesecond aspect.

Preferably, the ligand according to the second aspect is that of formula(IIa):

wherein:R₁ is tertiary butyl; R₂ is hydrogen; R₃ is 2,2-dimethylpropylene; andR₄ is selected from methyl, ethyl, propyl, or butyl.

Preferably in formula IV, R1 is tertiary butyl; R₂ is hydrogen; R₃ is2,2-dimethylpropylene.

In a fifth aspect of the invention, the catalysts of the first aspectare capable of polymerising (i) carbon dioxide and an epoxide, (ii) anepoxide and an anhydride, and (iii) a lactide and/or a lactone.Therefore, in a fifth aspect of the invention there is provided aprocess for the reaction of carbon dioxide with an epoxide, an anhydridewith an epoxide, or a lactide and/or a lactone in the presence of acatalyst according to the first aspect.

The process of the fifth aspect may be carried out in the presence of achain transfer agent. Suitable chain transfer agents include the chaintransfer agents, for example as defined by formula (II), in WO2013/034750, the entire contents of which are hereby incorporated byreference. For example, the chain transfer agent may be water, or maycomprise at least one amine (—NHR), alcohol (—OH) or thiol (—SH) moiety.

Examples of chain transfer agents useful in the second aspect includewater, mono-alcohols (i.e. alcohols with one OH group, for example,4-ethylbenzenesulfonic acid, methanol, ethanol, propanol, butanol,pentanol, hexanol, phenol, cyclohexanol), diols (for example,1,2-ethanediol, 1-2-propanediol, 1,3-propanediol, 1,2-butanediol,1-3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,2-diphenol, 1,3-diphenol, 1,4-diphenol, catechol and cyclohexenediol),triols (glycerol, benzenetriol, 1,2,4-butanetriol,tris(methylalcohol)propane, tris(methylalcohol)ethane,tris(methylalcohol)nitropropane, trimethylolpropane, preferably glycerolor benzenetriol), tetraols (for example, calix[4]arene,2,2-bis(methylalcohol)-1,3-propanediol, di(trimethylolpropane)), polyols(for example, D-(+)-glucose, dipentaerythritol or D-sorbitol), dihydroxyterminated polyesters (for example polylactic acid), dihydroxyterminated polyethers (for example poly(ethylene glycol)), acids (suchas diphenylphosphinic acid), starch, lignin, mono-amines (i.e.methylamine, dimethylamine, ethylamine, diethylamine, propylamine,dipropylamine, butylamine, dibutylamine, pentylamine, dipentylamine,hexylamine, dihexylamine), diamines (for example 1,4-butanediamine),triamines, diamine terminated polyethers, diamine terminated polyesters,mono-carboxylic acids (for example, 3,5-di-tert-butylbenzoic acid),dicarboxylic acids (for example, maleic acid, malonic acid, succinicacid, glutaric acid or terephthalic acid, preferably maleic acid,malonic acid, succinic acid, glutaric acid), tricarboxylic acids (forexample, citric acid, 1,3,5-benzenetricarboxylic acid or1,3,5-cyclohexanetricarboxylic acid, preferably citric acid),mono-thiols, dithoils, trithiols, and compounds having a mixture ofhydroxyl, amine, carboxylic acid and thiol groups, for example lacticacid, glycolic acid, 3-hydroxypropionic acid, natural amino acids,unnatural amino acids, monosaccharides, disaccharides, oligosaccharidesand polysaccharides (including pyranose and furanose forms). Preferably,the chain transfer agent is selected from cyclohexene diol,1,2,4-butanetriol, tris(methylalcohol)propane,tri(methylalcohol)propane, tri(methylalcohol)butane, pentaerythritol,poly(propylene glycol), glycerol, mono- and di-ethylene glycol,propylene glycol, tris(methylalcohol)nitropropane,tris(methylalcohol)ethane, 2,2-bis(methylalcohol)-1,3-propanediol,1,3,5-benzenetricarboxylic acid, 1,3,5-cyclohexanetricarboxylic acid,1,4-butanediamine, 1,6-hexanediol, D-sorbitol, 1-butylamine,terephthalic acid, D-(+)-glucose, 3,5-di-tert-butylbenzoic acid, andwater.

The process of the fifth aspect may be carried out in the presence of asolvent. Examples of solvents useful in the third aspect includetoluene, diethyl carbonate, dimethyl carbonate, dioxane,dichlorobenzene, methylene chloride, propylene carbonate, ethylenecarbonate, acetone, ethyl acetate, tetrahydrofuran (THF), etc.

When the process of the fifth aspect involves the reaction of anepoxide, the epoxide may be any compound comprising an epoxide moiety.The epoxide may be purified (for example by distillation, such as overcalcium hydride) prior to reaction with carbon dioxide or the anhydride.For example, the epoxide may be distilled prior to being added to thereaction mixture comprising the catalyst.

The process of the fifth aspect of the invention may be carried out at apressure of 1 to 100 atmospheres, preferably at 1 to 40 atmospheres,such as at 1 to 20 atmospheres, more preferably at 1 or 10 atmospheres.The catalysts used in the process of the second aspect allow thereaction to be carried out at low pressures.

The process of the fifth aspect of the invention may be carried out at atemperature of about 0° C. to about 250° C., preferably from about 40°C. to about 160° C., even more preferably from about 50° C. to about120° C. The duration of the process may be up to 168 hours, such as fromabout 1 minute to about 24 hours, for example from about 5 minutes toabout 12 hours, e.g. from about 1 to about 6 hours.

The process temperature, for copolymerisations of carbon dioxide and anepoxide, may be used to control the product composition. When thetemperature of the process of the fifth aspect which involves reactingcarbon dioxide and an epoxide is increased, the selectivity of thecatalyst towards the formation of cyclic carbonate is also increased.The catalysts and processes may operate at temperatures up to 250° C.

The process of the fifth aspect of the invention may be carried out atlow catalytic loading. For example, when the reaction involvescopolymerisation of carbon dioxide and an epoxide, the catalytic loadingfor the process is preferably in the range of 1:1,000-300,000catalyst:epoxide, more preferably in the region of 1:10,000-100,000catalyst:epoxide, even more preferably in the region of 1:50,000-100,000catalyst:epoxide. When the process involves copolymerisation of anepoxide and an anhydride, or the reaction of a lactide and/or lactone,the catalytic loading for the process is preferably in the range of1:1,000-300,000 catalyst:total monomer content, more preferably in theregion of 1:10,000-100,000 catalyst:total monomer content, even morepreferably in the region of 1:50,000-100,000 catalyst:total monomercontent. The ratios above are molar ratios.

The catalysts of the first aspect, and in particular catalysts whereinboth M₁ and M₂ are selected from Ni(II) and Mg(II), have high activityand selectivity for producing polycarbonates by reacting carbon dioxideand an epoxide, optionally in the presence of a chain transfer agent,and preferably at temperatures between about 40° C. to about 160° C.Thus, the reaction times for the process of the second aspect can beless than 12 hours, and preferably from about 2 to about 6 hours.

The process of the fifth aspect can be carried out in a batch reactor ora continuous reactor.

It will be appreciated that the various features described above for theprocess of the fifth aspect may be present in combination mutatismutandis. All preferred features of the first aspect apply equally tothe fifth aspect and may be present in combination mutatis mutandis.

The sixth aspect of the invention provides a product of the process ofthe fifth aspect of the invention. All preferred features of the fifthaspect of the invention apply to the sixth aspect of the inventionmutatis mutandis.

When the process of the fifth aspect is carried out in the presence of achain transfer agent, it produces polymer chains which are terminated atsubstantially all ends with hydroxyl groups (i.e. polycarbonate polyolsor polyester polyols). By “substantially”, it is meant that at least 90%of the resultant polymer chains, preferably at least 95% of theresultant polymer chains, and even more preferably at least 98%, andeven more preferably at least about 99% of the resultant polymer chainsare terminated at all ends in hydroxyl groups. In order for at least 90%of the resultant polymer chains to be terminated at all ends withhydroxyl groups, it is preferred for the process of the second aspect tobe carried out in the presence of at least about 4 equivalents of chaintransfer agent, relative to the amount of catalyst. In order for atleast 95% of the resultant polymer chains to be terminated at all endswith hydroxyl groups, it is preferred for the process of the secondaspect to be carried out in the presence of at least about 10equivalents of chain transfer agent, relative to the amount of catalyst.In order for at least 98% of the resultant polymer chains to beterminated at all ends with hydroxyl groups, it is preferred for theprocess of the fifth aspect to be carried out in the presence of atleast about 20 equivalents of chain transfer agent, relative to theamount of catalyst. Thus, polyols obtained by the process of the fifthaspect are considered to form part of the sixth aspect of the invention.

The chain transfer agent referred to in the fifth aspect may be used tocontrol the molecular weight (M_(n)) of the polymer products of thesixth aspect. Preferably, the molecular weight (M_(n)) of the polymerproducts of the sixth aspect is greater than about 200 g/mol. Themolecular weight (M_(n)) of the polymer products of the sixth aspect maybe from about 200 g/mol to about 200,000 g/mol. The molecular weight ofthe polymers produced by the fifth aspect can be measured by GelPermeation Chromatography (GPC) using, for example, a GPC-60manufactured by Polymer Labs, using THF as the eluent at a flow rate of1 ml/min on Mixed B columns, manufactured by Polymer Labs. Narrowmolecular weight polystyrene standards can be used to calibrate theinstrument.

It is possible to produce polycarbonate polyols and polyester polyolshaving a M_(n) of from about 200 g/mol to about 20,000 g/mol, preferablyless than about 10,000 g/mol by adding a chain transfer agent to theprocess of the fifth aspect.

It is also possible to produce polymers having a M_(n) of greater thanabout 20,000 g/mol from the process of the fifth aspect. Preferably, thepolymer having a M_(n) of greater than about 20,000 g/mol is apolycarbonate or a polyester, even more preferably a polycarbonate.Preferably, the polymer having a M_(n) of greater than about 20,000g/mol is a polycarbonate and is produced carrying out the process of thefifth aspect without adding a chain transfer agent (CTA).

The polymers produced by the fifth aspect may be produced to have apolydispersity index (PDI) of less than about 2, more preferably lessthan about 1.5, and even more preferably less than about 1.2.Furthermore, it is possible to control the molecular weight distributionso as to produce multi-modal or broad molecular weight distributionpolymers by addition of one or more chain transfer agent(s).

The polymers produced by the process of the fifth aspect (e.g.polycarbonates such as PCHC or PPC), are useful building blocks in thepreparation of various copolymeric materials. The polymers produced bythe process of the fifth aspect may undergo further reaction, forexample to produce polymeric products such as polyureas or polyamines.These processes and reactions are well known to the skilled person (forexample, refer to WO2013/034750).

The polycarbonate or polyester polyols produced by the process of thefifth aspect may be used in various applications and products whichconventionally use polyols, including adhesives (such as hot meltadhesives and structural adhesives), a binder (such as forest productbinders, foundry core binders and rubber crumb binders), coatings (suchas powder coatings, transport, e.g. automotive or marine coatings, fastcure coatings, self-healing coatings, top coats and primers, varnishes,and coatings for marine applications, e.g. oil rigs), elastomers (suchas cast elastomers, fibres/spandex elastomers, footwear elastomers,RIM/RRIM elastomers, synthetic leather elastomers, technicalmicrocellular elastomers and TPU elastomers), flexible foams (such asviscoelastic foams), rigid foams (such as rigid and flexible panels,moulded rigid foams, aerosol gap filling foam, spray foams,refrigeration foams, pour-in-place foams, and foam slabs) and sealants(such as glazing sealants for commercial, industrial and transport (e.g.automotive) applications, and construction sealants). The polyamines andpolyureas can be processed using methods standard techniques known inthe art, such as foaming.

It will be understood that the polycarbonate and polyester polyolsproduced by the process of the fifth aspect may be mixed with otherpolyols prior to further use or reaction.

The polycarbonates, and in particular, polycarbonates having a M_(n) ofgreater than about 20,000 g/mol (e.g. produced without adding chaintransfer agent to the process of the fifth aspect) may have a number ofbeneficial properties including high strength, high toughness, highgloss, high transparency, low haze, high gas (e.g. oxygen and carbondioxide) or water barrier properties, flame resistance, UV resistance,high durability, rigidity and stiffness, compatibility withplasticizers, broad dimensional stability temperature, biodegradabilityand biocompatibility, and modulus of elasticity and yield strengthcomparable to LDPE. Thus, these polymers may be used in variousapplications and products, such as electronic components, constructionmaterials, data storage products, automotive and aircraft products,security components, medical applications, mobile phones, packaging(including bottles), optical applications (such as safety glass,windscreens, etc).

EXAMPLE Example 1: Synthesis of Asymmetric Ligands H₂L¹⁻⁴

Ligands H₂L¹⁻⁴ were prepared by the following method:

A tetraaminophenol ligand may be formed by the following process (steps1 and 2):

To a round-bottomed flask was added 4-tert-butyl-2,6-diformylphenol(1.20 g, 5.80 mmol), NaClO₄ (2.81 g, 23.2 mmol), acetic acid (0.66 mL,11.6 mmol) and methanol (90 mL). This solution was heated to 70° C.whilst stirring, as the solution started to boil,2,2-dimethyl-1,3-propanediamine (0.70 mL, 5.8 mmol) was added slowly inmethanol (30 mL). The yellow reaction mixture was allowed to cool toroom temperature, and left stirring for 24 hours, after which a brightorange precipitate was filtered and washed with cold (−78° C.) methanol(1.85 g, 95%). The product was suspended in methanol (180 mL). Thesuspension was cooled to 0° C. and NaBH₄ (2.65 g, 69.9 mmol) was addedslowly. As NaBH₄ was added, the red-orange suspension turned to a clearsolution. Water was added slowly, and the solution turned cloudy. Onceprecipitate started to form, the mixture was left overnight and H₂L¹¹was filtered off as a white solid (1.21 g, 88%).

To a solution of the resulting product (20.8 mmol) in methanol (500 mL)was added a formaldehyde solution (37% in water, 104 mmol) at roomtemperature (RT). The reaction was stirred at RT for 15 h after whichthe reaction mixture was filtered and the filter cake was washed withMeOH and water. The resultant white powder was transferred to a roundbottom flask. Toluene was added and evaporated under reduced pressure toazeotrope off the residual water giving the desired product as a whitepowder (17.2 mmol). R₄X (iodomethane, iodoethane, 1-iodopropane or1-iodobutane, 104 mmol) was added to a stirred solution of this whitepowder (10.4 mmol) in anhydrous THF (120 mL) at 25° C. until thereaction was deemed to be complete. A white precipitate formed in thereaction mixture and was collected by suction filtration. The filtercake was washed with THF. The resultant white powder was transferred toa round bottom flask and dried under high vacuum for several hours. Thiswas dissolved (7.3 mmol) in MeOH and concentrated HCl_((aq)) (1:1) andplaced in a heating block set to 75° C. whilst refluxing and stirred for15 h. After this time, the slightly yellow solution was allowed to coolto RT and was neutralized with a saturated aqueous solution of K₂CO₃,inducing the product to precipitate out of solution as a white solid.This solid was collected and dried.

H₂L¹: ¹H NMR (400 MHz, CDCl₃) δ 7.05 (d, J=2.4 Hz, 1H), 7.02 (d, J=2.4Hz, 1H), 6.89 (d, J=2.5 Hz, 1H), 6.85 (d, J=2.5 Hz, 1H), 3.74 (s, 2H),3.61 (s, 2H), 3.54 (s, 2H), 3.51 (s, 2H), 2.50 (s, 2H), 2.39 (s, 2H),2.37 (s, 2H), 2.29 (s, 2H), 2.27 (s, 3H), 1.30 (3) (s, 9H), 1.29 (6) (s,9H), 0.93 (s, 6H), 0.92 (s, 6H).

MS (ESI) m/z: 567.5 ([M+H]⁺, 100%).

H₂L²: ¹H NMR (400 MHz, CDCl₃) δ 7.08 (m, 2H), 6.87 (m, 2H), 3.77 (s,2H), 3.58 (s, 2H), 3.53 (s, 4H), 2.55 (s, 2H), 2.53 (q, J=7.0 Hz, 2H),2.41 (s, 2H), 2.33 (s, 4H), 1.34 (s, 9H), 1.33 (s, 9H), 1.07 (t, J=7.0Hz, 3H), 0.94 (s, 6H), 0.92 (s, 6H).

MS (ESI) m/z: 581.5 ([M+H]⁺, 100%).

H₂L³: ¹H NMR (400 MHz, CDCl₃) δ 7.11 (m, 2H), 6.84 (m, 2H), 3.76 (s,2H), 3.52 (s, 2H), 3.50 (m, 4H), 2.54 (s, 2H), 2.48 (m, 2H), 2.38 (s,2H), 2.32 (s, 2H), 2.30 (s, 2H), 2.20 (s, 2H), 1.59 (m, 2H), 1.34 (s,18H), 0.93 (s, 6H), 0.91 (s, 6H).

MS (ESI) m/z: 595.5 ([M+H]⁺, 100%), 581.5 ([M-CH₃+H]⁺, 30%).

H₂L⁴: ¹H NMR (400 MHz, CDCl₃) δ 7.11 (m, 2H), 6.83 (m, 2H), 3.75 (s,2H), 3.51 (m, 6H), 2.53 (s, 2H), 2.49 (m, 2H), 2.38 (s, 2H), 2.32 (s,2H), 2.30 (s, 2H), 1.55 (m, 2H), 1.34 (s, 18H), 0.94 (q, J=7.3 Hz, 3H),0.93 (s, 6H), 0.91 (s, 6H).

MS (ESI) m/z: 609.5 ([M+H]⁺, 100%), 595.5 ([M-CH₃+H]⁺, 10%), 581.5([M-CH₂CH₃+H]⁺, 10%).

Example 2: Synthesis of Asymmetric Ligand H₂L⁵

4-tert-butyl-2,6-diformylphenol (4 mmol) and1,3-diamino-2,2-dimethylpropane (2 mmol) were each dissolved in EtOH (15mL and 10 mL respectively). The solutions were warmed to boiling thenthe solution of amine added dropwise with stirring giving an immediatecolour change to a deeper yellow. After stirring overnight theprecipitate was collected, washed with cold ethanol (2×5 mL), pentane(1×5 mL) then dried under vacuum, giving 4. ¹H NMR (CDCl₃) δ: 14.45 (brs, 2H), 10.56 (s, 2H), 8.45 (s, 2H), 7.94 (s, 2H), 7.55 (s, 2H), 3.58(s, 4H), 1.34 (s, 18H), 1.15 (s, 6H).

4 (0.4 mmol) was dissolved in THF (10 mL) and treated with LiHMDS (0.8mmol) in THE (3 mL) causing the bright yellow solution to change to agreenish yellow solution. After 30 mins a solution of 1,2-diaminobenzene(0.4 mmol) was added in THF (10 mL) over 10 mins with rapid stirring.After stirring overnight the colour had again returned to bright yellow.The solution was concentrated to 2 mL and layered with heptane (10 mL)and allowed to stand. The yellow solid that precipitated after 1 day wascollected and washed with pentane (2×5 mL) then dried under vacuum. ¹HNMR (CDCl₃) δ: 9.51 (s, 2H), 7.91 (s, 2H), 7.45 (d, 2H), 7.38 (d, 2H),6.74 (s, 4H), 3.4 (br s, 4H), 1.34 (s, 18H), 0.62 (s, 6H).

5 (0.2 mmol) was dissolved in dry MeOH (25 mL) under nitrogen in a dried3-neck round-bottomed flask. HCl in EtOH was added (1.2 mmol) and thesolution stirred for 10 minutes before NaBH₄ (2 mmol) was added inportions. The solution was stirred for 2 hours after which the solventwas removed under vacuum. Water (20 mL) was added to the crude and thepH brought up to 6-7 by adding AcOH dropwise. The product (H₂L⁵¹⁰) wasextracted with DCM (2×25 mL), dried over NaSO₄ and the solvent removedunder vacuum.

¹H NMR (CDCl₃) δ: 7.2-7.35 (m, 2H), 7.19 (s, 1H), 7.01 (s, 1H),6.85-6.95 (m, 4H), 4.32 (s, 4H), 4.26 (br s, 2H), 4.08 (s, 2H), 2.59 (s,4H), 2.42 (s, 2H), 1.32 (s, 18H), 1.16 (s, 6H). ¹³C NMR (CDCl₃) δ:154.4, 141.7, 138.0, 129.2, 128.4, 126.9, 125.4, 125.1, 124.9, 122.4,119.2, 111.3, 59.5, 54.2, 46.5, 35.1, 34.1, 31.7, 24.6.

Example 3: Synthesis of Asymmetric Ligand H₂L⁶

The asymmetric ligand H₂L⁶ was prepared using the following method:

B was formed by reacting 4-tert-butylsalicylaldehyde (15 mmol) withpiperazine (7.5 mmol) and formaldehyde (15 mmol) in glacial acetic acid(25 mL) at 120° C. The white precipitate was collected and washed withethanol and diethyl ether.

A solution of 2,2-dimethyl-1,3-propanediamine (6.4 mmol) in MeOH (60 mL)was added dropwise over 6 h to a refluxing solution of B(6.4 mmol) inMeOH (300 mL). After a further 10 h reflux, the solution was cooled toRT and the bright yellow supernatant decanted from a bright yellowsolid. The residue was re-dissolved in DCM and co-evaporated with MeOHuntil a yellow precipitate formed. The resulting solids were collectedby filtration, washed with MeOH, pentane and dried under high vacuum for2 h. This gave a yellow powder (5.0 mmol). A solution of this yellowpowder in THF/MeOH (3:1) was treated with solid NaBH₄. The resultingwhite suspension was allowed to stir for 1 h at RT, then partitionedbetween NaHCO₃ (2M, aq) and DCM. The organic phase was separated anddried over Na₂SO₄, then evaporated to dryness to yield H₂L⁶.

H₂L⁶: ¹H NMR (400 MHz, CDCl₃) δ 7.14-7.05 (m, 2H), 7.05-6.96 (m, 2H),5.37-5.27 (s, 4H), 3.89-3.81 (s, 4H), 3.70-3.63 (s, 4H), 2.67-2.62 (s,4H), 2.55-2.49 (s, 2H), 1.35 (s, 18H), 0.99-0.90 (s, 6H).

Example 4: Synthesis of Asymmetric Ligand H₂L⁷

The asymmetric ligand H₂L⁷ was prepared using the following method:

C was prepared by reacting 4-tert-butylsalicylaldehyde (129 mmol) withformaldehyde (193 mmol) in HBr (48% aq, 970 mmol) with a few catalyticdrops of H₂SO₄ at 70° C. for 16 hours. The solution was cooled, dilutedand extracted with methylene chloride (30 mL), giving C.N,N′-dimethyl-2,2-dimethyl-1,3-propanediamine was prepared by reactionof 2,2-dimethyl-1,3-propanediamine (166 mmol) with ethyl formate (80 mL)followed by reduction with LiAlH₄ (10 g) in diethyl ether (250 mL).

A solution of 3-(bromomethyl)-2-hydroxy-5-tert-butylbenzaldehyde C (48.4mmol) in THF (40 mL) was added to a stirred solution ofN,N′-dimethyl-2,2-dimethyl-1,3-propanediamine (22.0 mmol) in THF (20 mL)giving a yellow suspension. A solution of triethylamine (61.6 mmol) inTHF (10 mL) was added dropwise. The reaction mixture was stirred for 2 hafter which time it was partitioned between EtOAc and water. The organicextracts were combined, and dried over Na₂SO₄ before evaporation todryness to yield an orange oil. The crude product was dissolved in MeOH(50 mL) and treated with a solution of LiOH (88 mmol) in MeOH (75 mL).After standing overnight the yellow crystalline precipitate was isolatedby filtration, washed with ice cold MeOH and dried under high vacuumovernight. This gave a yellow microcrystalline solid (27.6 mmol). Asolution of 2,2-dimethyl-1,3-propanediamine (3.52 mmol) in EtOH (18 mL)was added dropwise over 6 h to a suspension of the latter yellowmicrocrystalline solid (3.49 mmol) and the resulting yellow solution wasallowed to stir for a further 8 h. The solvent was removed completelyand the yellow solid residue was suspended in pentane and collected byfiltration, washed with pentane and dried under high vacuum for 2 h.This gave a yellow powder (2.8 mmol). A suspension of this yellow powderin dry EtOH was treated with a solution of HCl in diethyl ether (2M).Next, solid NaBH₄ was added in one portion. The resulting whitesuspension was allowed to stir for 1 h at RT then partitioned betweenNaHCO₃ (2M, aq) and DCM. The organic phase was separated and dried overNa₂SO₄ then evaporated to dryness to yield H₂L⁷.

H₂L⁷: ¹H NMR (400 MHz, CDCl₃) δ 7.05-6.95 (m, 4H), 5.37-5.27 (s, 4H),3.81-3.74 (s, 4H), 3.72-3.65 (s, 4H), 2.52-2.45 (s, 4H), 2.45-2.40 (s,4H), 2.29-2.24 (s, 6H), 1.34-1.24 (s, 18H), 1.01-0.92 (d, J=5.5 Hz, 6H).

Example 5: Synthesis of asymmetric ligands Li₂L_(imine) ⁸⁻¹⁰ and H₂L⁹⁻¹⁰

The asymmetric ligands Li₂L_(imine) ⁸⁻¹⁰ and H₂L⁹⁻¹⁰ were prepared usingthe following method:

Preparation of Li₂L_(imine) ⁸⁻¹⁰:

To a solution of D (56.3 mmol) in EtOH (500 mL) was added2,2-dimethyl-1,3-propanediamine (28.2 mmol) and MgSO₄ (281.5 mmol).Reaction mixture was stirred 3 h at RT. After this time, reaction mediumwas filtered, filter cake was washed with DCM, and the mother liquor wasevaporated in vacuo to yield a yellow solid. The latter was solubilisedin MeOH, and the reaction medium was cooled to 0° C. NaBH₄ (258.0 mmol)was added by portion. Reaction mixture was allowed to stir overnight atRT. After this time, solvents were evaporated in vacuo. DCM and waterwere added, phases were separated, and the aqueous phase was extractedwith DCM. The organic layers were combined and dried over Na₂SO₄.

Solvents were evaporated in vacuo to yield a product that was purifiedby recrystallization (DCM/MeOH, 20.9 mmol). To a solution of thispurified product (17.5 mmol) in THF (200 mL) was added HCl (1M, 400 mL).Reaction mixture was refluxed overnight. After this time, DCM was added,phases were separated, and the aqueous phase was extracted with DCM. Theorganic layers were combined and dried over Na₂SO₄. Solvents wereevaporated in vacuo to yield a crude product that was purified byrecrystallization (DCM/heptane, 15.9 mmol). The latter product (9 mmol)was next solubilised in MeOH (150 mL) and LIOH (36 mmol) was added.Reaction mixture was stirred for 1 h at RT. After this time, a yellowprecipitate had formed, was collected by filtration, and washed withice-cold MeOH. To a suspension of this yellow product (1 equiv.) in MeOHwas added dropwise and over 6 h a solution of the appropriate diamine(2,2-dimethyl-1,3-propanediamine, 1,3-propanediamine or ethylenediamine,1 equiv.) in MeOH at RT. Reaction mixture was then stirred overnight atRT. After this time, a yellow precipitate had formed, was collected byfiltration, and washed with ice-cold MeOH. Products were identified asLi₂L_(imine) ⁸¹⁰.

Preparation of H₂L⁹⁻¹⁰:

To a suspension of Li₂L_(imine) ⁹⁻¹⁰ (1 equiv.) in MeOH was added HCl(1.25M in EtOH, 6 equiv.) and NaBH₄ (20 equiv.). Reaction mixture wasstirred overnight at RT. After this time, solvents were evaporated invacuo. DCM and water were added, phases were separated, and the aqueousphase was extracted with DCM. The organic layers were combined, washedwith brine and dried over Na₂SO₄. Solvents were evaporated in vacuo toyield H₂L⁹⁻¹⁰.

H₂L⁹: ¹H NMR (400 MHz, CDCl₃) δ 6.96 (d, J=2.5 Hz, 2H), 6.95 (d, J=2.5Hz, 2H), 3.83 (s, 8H), 2.65 (t, J=6.5 Hz, 4H), 2.51 (s, 4H), 1.78-1.73(m, 2H), 1.25 (s, 18H), 1.01 (s, 6H).

MS (ESI) m/z: 525.4 ([M+H]⁺, 100%)

H₂L¹⁰: ¹H NMR (400 MHz, CDCl₃) δ 6.97 (d, J=2.5 Hz, 2H), 6.95 (d, J=2.5Hz, 2H), 3.82 (s, 4H), 3.80 (s, 4H), 2.84 (s, 4H), 2.52 (s, 4H), 1.26(s, 18H), 0.97 (s, 6H). MS (ESI) m/z: 511.3 ([M+H]⁺, 100%)

Example 6: synthesis of asymmetric ligands H₂L¹²⁻¹³

The asymmetric ligands H₂L¹²⁻¹³ were prepared using the followingmethods:

For the preparation of H₂L¹¹, see example 1.

Preparation of H₂L¹²:

To a solution of H₂L¹¹ (5.4 mmol) in MeOH (100 mL) was addedbenzaldehyde (6.5 mmol) and the reaction stirred at RT for 3 h. Thewhite precipitate formed was isolated by filtration and washed with coldMeOH (3.78 mmol). A solution of this white product (0.78 mmol) in MeOH(10 mL) and DCM (5 mL) was treated with methyl acrylate (0.94 mmol) andthe reaction stirred at RT for 16 h after which the solvent was removedin vacuo to yield a white powder (0.74 mmol). To a solution of thiswhite powder (0.14 mmol) in THF (10 mL) was added aq. 1M HCl until pH 3was obtained (ca. 4 mL) and the reaction stirred at RT for 3 h.Neutralisation with aq. K₂CO₃ followed by extraction with DCM affordedH₂L¹² (0.04 mmol).

MS (ES/CI) m/z: 639.4 ([M+H]⁺, 100%)

IR (ν_(C=O), cm⁻¹, neat): 3300, 2955, 2907, 2869, 1741, 1611, 1465,1395, 1362, 1298, 1216.

Preparation of H₂L¹³:

To a solution of H₂L¹¹ (9.0 mmol) in MeOH (125 mL) was added methylacrylate (19.0 mmol) and the reaction stirred at RT for 16 h. The whitesolid formed was isolated by filtration and washed with cold MeOH.Recrystallisation from hot EtOH gave H₂L¹³.

H₂L¹³: ¹H NMR (400 MHz, CDCl₃) δ 7.33 (d, J=2.5 Hz, 2H), 6.75 (d, J=2.5Hz, 2H), 3.75 (s, 6H), 3.42 (br s, 4H), 3.20 (br s, 4H), 2.94 (br s,4H), 2.69 (t, J=2.7 Hz, 4H), 2.32 (br s, 4H), 1.42 (s, 18H), 0.88 (s,12H), 0.24 (br s, 4H).

MS (ES/CI) m/z: 725.3 ([M]⁺, 100%)

IR (cm⁻¹, neat): 3301, 2955, 2907, 2869, 1741, 1480, 1216, 1100.

Example 7: synthesis of asymmetric ligands H₂L¹⁴⁻¹⁵

The ligands H₂L¹⁴⁻¹⁵ were prepared by the following method:

2,2-dimethyl-1,3-propanethiol (5 mmol) was added to a stirred anddegassed solution of KOH (20 mmol) in ethanol (50 ml). The mixture wasstirred until all components form a homogeneous solution. Then C (10mmol) was added as a solid to the reaction which slowly dissolves toform a bright yellow solution. The reaction was allowed to stir undernitrogen atmosphere for 20 h. 1M HCl_((aq)) was then added until thereaction mixture reached acidicity (pH=2) and formed a white suspension.This mixture was extracted with DCM, the organic extracts combined andconcentrated in vacuo to give an oil. This was purified on silica. Asolution of 2,2-dimethyl-1,3-propanediamine (3.4 mmol) in MeOH (100 ml)was added dropwise to a stirred solution of this purified oil (2.8 mmol)in MeOH (200 ml) at RT under air. The reaction was allowed to stir for20 h at RT, during which time a yellow precipitate formed. Theprecipitate was collected by filtration and washed with cold MeOH,affording a yellow solid. A MeOH solution (50 mL) of this yellow product(1.9 mmol) was prepared under nitrogen and allowed to stir at RT. Undera flow of nitrogen, NaBH₄ (19.0 mmol) was added portion-wise as a solidand the mixture allowed to stir for a further 16 h. The resultingcolourless solution was then quenched by the addition of water. Themixture was extracted with EtOAc, the organic fractions combined, washedwith water and saturated aqueous NaCl solution and all volatiles wereremoved in vacuo to afford H₂L¹⁴

H₂L¹⁴: ¹H NMR (CDCl₃, 400.1 MHz): δ 7.16 (m, 2H), 6.89 (m, 2H), 3.93 (m,2H), 3.71 (m, 6H), 2.56 (s, 4H), 2.50 (s, 4H), 1.26 (s, 18H), 0.98 (d,12H)

MS (CI) m/z: 587.4 [M+H]⁺

1,3-propanedithiol (0.56 mL, 5.5 mmol) was dissolved in EtOH (50 mL) ina fumecupboard. A solution of C (3 g, 11.1 mmol) in EtOH (50 mL) wasadded dropwise over 15 minutes and the mixture stirred overnight. Thesolvent was removed under vacuum and distilled water (50 mL) was added.The product was extracted with DCM (2×30 mL), dried over NaSO₄ and thesolvent removed under vacuum. The product (was purified by columnchromatography (95:5 Cyclohexane:EtOAc) to give a light yellow oil (54%)¹H NMR (CDCl₃) δ: 11.22 (s, 2H), 9.90 (s, 2H), 7.60 (d, 2H), 7.45 (d,2H), 3.79 (s, 4H), 2.61 (t, 4H), 1.93 (q, 2H), 1.35 (s, 18H).

The half macrocycle (0.484 g, 0.99 mmol) was dissolved in MeOH (35 mL).A solution of 2,2-dimethyl-1,3-propane (0.12 mL, 0.99 mmol) in MeOH (25mL) was added dropwise over 30 minutes and the solution stirredovernight. A yellow precipitate was filtered off and washed with MeOH.¹H NMR (CDCl₃) δ: 13.74 (br s, 2H), 8.34 (s, 2H), 7.37 (s, 2H), 7.17 (s,2H), 3.83 (s, 4H), 3.48 (s, 4H), 2.64 (t, 4H), 1.98 (m, 2H), 1.31 (s,18H), 1.08 (s, 6H).

The yellow precipitate (0.25 g, 0.44 mmol) was dissolved in dry MeOH (50mL) before NaBH₄ (0.2 g, 4.4 mmol) was added in portions. The solutionwas stirred for 2 hours after which the solvent was removed undervacuum. Water (50 mL) was added to the crude and the pH brought up to6-7 by adding AcOH dropwise. The product (H₂L¹⁵) was extracted with DCM(2×25 mL), dried over NaSO4 and the solvent removed under vacuum.

¹H NMR (CDCl₃) δ: 7.22 (s, 2H), 6.88 (s, 2H), 4.01 (s, 4H), 3.66 (s,4H), 2.50 (s, 4H), 2.38 (t, 4H), 1.6 (q, 2H), 1.29 (s, 18H), 1.06 (s,6H). ¹³C NMR (CDCl₃) δ: 153.3, 141.6, 126.6, 125.3, 123.8, 121.0, 57.6,54.0, 34.7, 34.0, 31.6, 30.3, 29.8, 29.5, 24.5. ESI-MS: 559.3 ([M+H]⁺,100%).

Example 8: Synthesis of [L¹⁻¹⁵M₂(X₂)] catalysts

The complexes [L¹⁻¹⁵M₂(X₂)] were prepared using the following method:

General Procedure:

To a suspension of H₂L¹⁵ (1 equiv.) in MeOH was added the appropriatemetal precursor M(X)₂ (2 equiv.; Ni(OAc)₂.4H₂O, Mg(OAc)₂.4H₂O orZn(OAc)₂.2H₂O). Reaction mixture was stirred overnight at RT. After thistime, solvents were evaporated and excess water/AcOH was removed byazeotrope with toluene to yield the desired complexes [L¹⁻¹⁵M₂(X)₂].

[L¹Ni₂(OAc)₂]: MS (ES) m/z: 741.3 ([M−OAc]⁺, 100%).

IR (ν_(C=O), cm⁻¹, neat): 1581, 1410.

[L²Ni₂(OAc)₂]: MS (ES/CI) m/z: 753.2 ([M−OAc]⁺, 100%).

IR (ν_(C=O), cm⁻¹, neat): 1581, 1413.

[L²Zn₂(OAc)₂]: MS (ES/CI) m/z: 751.2 ([M−2AcO⁻+HCO₂ ⁻]⁺, 100%).

IR (ν_(C=O), cm⁻¹, neat): 1603, 1383.

[L³Ni₂(OAc)₂]: MS (ES/CI) m/z: 767.2 ([M−OAc]⁺, 100%).

IR (ν_(C=O), cm⁻¹, neat): 1581, 1413.

[L³Mg₂(OAc)₂]: ¹H NMR (400 MHz, MeOD) δ 7.02 (m, 4H), 3.74 (d, J=18.9Hz, 4H), 3.6 (d, J=8.9 Hz, 4H), 2.46 (d, J=8.7 Hz, 4H), 2.44 (m, 2H),2.41 (d, J=8.7 Hz, 2H), 1.90 (s, 6H), 1.54 (m, 2H), 1.30 (s, 9H), 1.28(s, 9H), 0.96 (s, 6H), 0.95 (s, 6H), 0.84 (t, J=7.3 Hz, 3H).

MS (ES/CI) m/z: 685.3 ([M−2OAc]⁺, 100%).

IR (ν_(C=O), cm⁻¹, neat): 1607, 1395.

[L⁴Ni₂(OAc)₂]: MS (ES/CI) m/z: 781.2 ([M−OAc]⁺, 100%).

IR (ν_(C=O), cm⁻¹, neat): 1581, 1413.

[L⁷Ni₂(OAc)₂]: MS (ES/CI) m/z: 739.2 ([M−2OAc+O₂CH]⁺, 100%).

IR (ν_(C=O), cm⁻¹, neat): 1581, 1414.

[L⁹Mg₂(OAc)₂]: ¹H NMR (400 MHz, CD₃OD) δ 7.01 (s, 4H), 4.00 (d, J=3.6Hz, 2H), 3.97 (d, J=3.7 Hz, 2H), 3.27 (d, J=12.0 Hz, 2H), 3.21 (d,J=12.0 Hz, 2H), 3.05-2.99 (m, 2H), 2.79-2.70 (m, 4H), 2.64 (d, J=11.6Hz, 2H), 1.94-1.76 (m, br, 4H), 1.25 (s, 18H), 1.23 (s, 3H), 1.01 (s,3H).

MS (ESI) m/z: 615.3 ([M−2AcO⁻+HCO₂ ⁻]⁺, 100%).

[L⁹Ni₂(OAc)₂]: MS (ESI) m/z: 683.2 ([M−2AcO⁻+HCO₂ ⁻]⁺, 100%). IR(ν_(C=O), cm⁻¹, neat): 1566, 1477.

[L⁹Ni₂(OAc)₂]: MS (ESI) m/z: 683.2 ([M−2AcO+HCO₂ ⁻]⁺, 100%). IR(ν_(C=O), cm⁻¹, neat): 1566, 1477.

[L¹⁰Ni₂(OAc)₂]: MS (ESI) m/z: 669.1 ([M−2OAc+O₂CH]⁺, 100%). IR (ν_(C=O),cm⁻¹, neat): 1566, 1477.

[L¹³Ni₂(OAc)₂]: MS (ES/CI) m/z: 855.2 ([M−2AcO⁻−2CH₃+HCO₂]⁺, 100%),809.2 ([M−2AcO⁻−2CH₃+1 HCO₂ ⁻]⁺, 80%).

IR (ν_(C=O), cm⁻¹, neat): 1573, 1480.

[L¹⁴Ni₂(OAc)₂]: IR (ν_(C=O), cm⁻¹, neat): 1566 and 1413.

[L¹⁵Ni₂(OAc)₂]: MS (CI) m/z: 717 ([M−2AcO⁻+HCO₂ ⁻]⁺, 100%).

IR (ν_(C=O), cm⁻¹, neat): 1562 and 1410.

Example 9: Synthesis of [L_(imine) ⁸Mg₂(OAc)₂] Complex

The complex [L_(imine) ⁸Mg₂(OAc)₂] was prepared using the followingmethod:

Preparation of [L_(imine) ⁸M₂(OAc)₂]:

To a suspension of Li₂L_(imine) ⁸ (1 equiv.) in MeOH was addedMg(OAc)₂.4H₂O (2 equiv.). Reaction mixture was stirred overnight at RT.After this time, solvents were evaporated. Pentane was added and thereaction mixture was filtered. Filtrate was evaporated to yield complex[L_(imine)Mg₂(OAc)₂] as a slightly yellow solid.

L_(imine) ⁸Mg₂(OAc)₂: ¹H NMR (400 MHz, CD₃OD) δ 8.13 (d, J=2.0 Hz, 2H),7.31 (d, J=2.7 Hz, 2H), 7.26 (d, J=2.7 Hz, 2H), 4.09-4.03 (m, 4H),3.31-3.26 (m, 2H), 2.86-2.79 (m, 2H), 2.66 (d, J=11.3 Hz, 2H), 2.22-2.14(m, 2H), 1.90-1.40 (s, br, 6H), 1.31 (s, 18H), 1.21 (s, 3H), 1.16 (s,3H), 1.14 (s, 3H), 1.02 (s, 3H).

MS (ESI) m/z: 639.3 ([M−2AcO⁻+HCO₂ ⁻], 100%).

Example 10: Polymerisation of CO₂ and CHO at 100° C. and 0.01 Mmol of[LM₂(OAc)₂]

[LM₂(OAc)₂] (0.01 or 0.025 mmol) was dissolved in cyclohexene oxide (25or 50 mmol) in a Schlenk. The vessel was degassed, charged with CO₂ (1bar) and heated at 100° C. with magnetic stirring for the right time,giving poly(cyclohexene carbonate). The polymer contained >99% carbonatelinkages and was produced with >99% selectivity in all cases. Theasymmetric ligands L1-L4 having N-substitution demonstrate superioractivity, productivity (turnover number) and activity under lowloadings. All the asymmetric complexes demonstrate excellent selectivityfor polymer, activity under low pressures and narrow polydispersitypolymers. The results are shown in Table 1.

TABLE 1 Copolymerisation of CHO and CO₂ using [LM₂(OAc)₂] Vol ConversionCHO T P Time (PCHC + Cyclic Catalyst cat:CHO (mL) (° C.) (bar) (h) vsCHO [L¹Ni₂(OAc)₂] 1:5000 5 100 1 3 44% [L¹Ni₂(OAc)₂] 1:1000 2.5 100 11.17 51.8 [L²Ni₂(OAc)₂] 1:5000 5 100 1 3 44% [L³Ni₂(OAc)₂] 1:5000 5 1001 3 47% [L⁴Ni₂(OAc)₂] 1:5000 5 100 1 3 48% [L_(imine) ⁸Mg₂(OAc)₂] 1:10002.5 100 1 4 32.55%    [L⁹Ni₂(OAc)₂] 1:1000 2.5 100 1 3 27.9%  [L⁹Mg₂(OAc)₂] 1:1000 2.5 100 1 3 43.23%    Selec- Catalyst tivity TONTOF PDI Mn [L¹Ni₂(OAc)₂] 100% 2203 734 1.254 12600 [L¹Ni₂(OAc)₂] 99.9% 518 443 1.018/ 16300/ 1.051 9200 [L²Ni₂(OAc)₂] 100% 2212 737 1.29 13100[L³Ni₂(OAc)₂] 100% 2370 790 1.234 12900 [L⁴Ni₂(OAc)₂] 100% 2381 7941.241 12900 [L_(imine) ⁸Mg₂(OAc)₂] 100% 326 81 [L⁹Ni₂(OAc)₂] 99.5%  27993 1.042/ 12700/ 1.095 5300 [L⁹Mg₂(OAc)₂] 100% 432 144 1.035/ 20400/1.196 6600

Example 11: Polymerisation of CO₂ and CHO at 130° C. and High Pressurewith [LM₂(OAc)₂]

[L^(x)M₂(OAc)₂] (0.0148 mmol) was added to a dried Schlenk tube anddried under vacuum for 60 minutes. CHO (15 mL, 148.26 mmol) was addedunder N₂ via a syringe, the mixture was transferred to a reactor underpressure 0.2 bar CO2. Reactor vessel was heated to 130° C., thenpressured to 10 bar and stirred for 1-2 hours, after which the vesselwas cooled to 5° C., the pressure slowly released and a sample taken forGPC/NMR analysis. The results are shown in Table 2.

TABLE 2 Comparison of catalytic activity of equivalent Ni and Mgcomplexes under identical conditions for CHO and CO₂ (10 bar)copolymerisation at 1:10,000 loading. Conversion Vol (PCHC + CHO T PTime Cyclic Selec- Catalyst cat:CHO (mL) (° C.) (bar) (h) vs CHO tivityTON TOF PDI Mn [L¹¹Mg₂(OAc)₂] 1:10000 15 130 10 2 44.2%  100% 4420 22101.192 15100 [L¹¹Ni₂(OAc)₂] 1:10000 15 130 10 2 51.6% 98.5% 5156 25781.264 29400 [L¹Ni₂(OAc)₂] 1:10000 15 130 10 1 44.5% 99.8% 4450 44501.234 21300

Although the symmetrical magnesium catalyst [L¹¹Mg₂(OAc)₂] and nickelcatalyst [L¹¹Ni₂(OAc)₂] perform well and have high selectivity andactivity (TOF) the asymmetric catalyst [L¹Ni₂(OAc)₂] has a far superioractivity and produces the same turn-over-number in half the time. Thisclearly demonstrates the unexpected benefits that an asymmetric catalystcan give over a symmetric catalyst.

Example 12: Polymerisation of CO₂ and PO with [LM₂(OAc)₂]

[L^(x)M₂(OAc)₂] (0.0043-0.21 mmol) was dissolved in propylene oxide (211mmol) in a Schlenk tube and the solution transferred into a pre-dried100 mL stainless steel Parr pressure vessel using a syringe. The vesselwas charged with CO₂ (20 bar) and heated to the desired temperature ° C.The solution was stirred mechanically for the desired time, givingpoly(propylene carbonate) as a white solid with a high selectivity forpolymer and >99% carbonate linkages. The catalysts showed excellentactivity, producing a high yield of polymer. The catalysts demonstratedsignificantly improved selectivity and activity when compared tosymmetric catalyst [L¹Ni₂(OAc)₂] and could be used at a much lowercatalyst loading. The results are shown in Table 3.

TABLE 3 Copolymerisation of PO and CO₂ using [LM₂(OAc)₂] Selectivity T PTime for Polymer Catalyst cat:PO (° C.) (bar) (h) polymer yield PDI Mn[L¹Ni₂(OAc)₂] 1:5000 80 20 9 85% 6.8 g 1.027/ 34000/ 1.032 16900[L²Ni₂(OAc)₂] 1:5000 80 20 9 89%   8 g 1.027/ 42600/ 1.030 21200[L³Ni₂(OAc)₂] 1:5000 80 20 9 87% 7.8 g 1.025/ 38900/ 1.028 19300[L¹Ni₂(OAc)₂] 1:1000 70 20 16 87%  19 g 1.034/ 44500/ 1.030 22300[L¹Ni₂(OAc)₂]  1:50000 90 20 16 80% 2.2 g 1.1 19700 [L⁷Ni₂(OAc)₂] 1:100080 20 1 90% 8.5 g 1.02/ 17000/ 1.03 8600 [L¹¹Ni₂(OAc)₂] 1:1000 80 20 1675% 10.4 g  1.12 15200

Example 13: Polymerisation of CO₂ and PO with [L¹Ni₂(OAc)₂] in thePresence of a Starter—PPG-425

[L¹Ni₂(OAc)₂] (0.21 mmol) and PPG-425 (4.3 mmol) was dissolved inpropylene oxide (211 mmol) in a Schlenk tube and the solutiontransferred into a pre-dried 100 mL stainless steel Parr pressure vesselusing a syringe. The vessel was charged with CO₂ (20 bar) and heated tothe 80° C. The solution was stirred mechanically for the 6 hrs, giving apoly(propylenecarbonate) diol (9.2 g) as a clear viscous oil with a highselectivity for polymer and >99% carbonate linkages.

Example 14: Polymerisation of CO₂ and PO with [L¹Ni₂(OAc)₂] in thePresence of a Starter—1,6-hexanediol

[L¹Ni₂(OAc)₂] (0.21 mmol) and 1,6-hexanediol (8.4 mmol) was dissolved inpropylene oxide (211 mmol) in a Schlenk tube and the solutiontransferred into a pre-dried 100 mL stainless steel Parr pressure vesselusing a syringe. The vessel was charged with CO₂ (20 bar) and heated tothe 80° C. The solution was stirred mechanically for 12 hrs, giving apoly(propylenecarbonate) diol (6.4 g) as a clear viscous oil with a highselectivity for polymer and >99% carbonate linkages.

Example 15: Polymerisation of CO₂ and PO with [L¹Ni₂(OAc)₂] in thePresence of a Solvent—toluene

[L¹Ni₂(OAc)₂] (0.021 mmol) was dissolved in propylene oxide (106 mmol)in a Schlenk tube and a further 7.5 mL of dry toluene was added and thesolution transferred into a pre-dried 100 mL stainless steel Parrpressure vessel using a syringe. The vessel was charged with CO₂ (20bar) and heated to the 80° C. The solution was stirred mechanically forthe 16 hrs, giving a toluene solution of poly(propylenecarbonate) whichwas isolated (5 g) as a white powder with a high selectivity for polymerand >99% carbonate linkages.

Example 16: Polymerisation of CO₂ and PO with [L¹Ni₂(OAc)₂] in thePresence of a Solvent—n-butyl acetate

[L¹Ni₂(OAc)₂] (0.021 mmol) was dissolved in propylene oxide (106 mmol)in a Schlenk tube and a further 7.5 mL of dry n-butyl acetate was addedand the solution transferred into a pre-dried 100 mL stainless steelParr pressure vessel using a syringe. The vessel was charged with CO₂(20 bar) and heated to the 80° C. The solution was stirred mechanicallyfor 16 hrs, giving an n-butyl acetate solution ofpoly(propylenecarbonate) which was isolated (4.7 g) as a white powderwith a high selectivity for polymer and >99% carbonate linkages.

Example 17: Polymerisation of CO₂ and Tert-Butyl Glycidyl Ether with[L¹Ni₂(OAc)₂]

[L¹Ni₂(OAc)₂] (0.105 mmol) was dissolved in tert-butyl glycidyl ether(105 mmol) in a Schlenk tube and the solution transferred into apre-dried 100 mL stainless steel Parr pressure vessel using a syringe.The vessel was charged with CO₂ (20 bar) and heated to the 80° C. Thesolution was stirred mechanically for 16 hrs, givingpoly(tert-butylether 1,2-glycerol carbonate) which was isolated (8.6 g)as a white powder with a high selectivity for polym for polymer and >99%carbonate linkages.

All of the features disclosed in this specification (including anyaccompanying claims, abstract and drawings), and/or all of the steps ofany method or process so disclosed, may be combined in any combination,except combinations where at least some of such features and/or stepsare mutually exclusive.

Each feature disclosed in this specification (including any accompanyingclaims, abstract and drawings) may be replaced by alternative featuresserving the same, equivalent or similar purpose, unless expressly statedotherwise. Thus, unless expressly stated otherwise, each featuredisclosed is one example only of a generic series of equivalent orsimilar features.

The invention is not restricted to the details of the foregoingembodiment(s). The invention extends to any novel one, or any novelcombination, of the features disclosed in this specification (includingany accompanying claims, abstract and drawings), or to any novel one, orany novel combination, of the steps of any method or process sodisclosed

1. A catalyst of formula (I):

wherein: M₁ and M₂ are independently selected from Zn(II), Cr(II),Co(II), Cu(II), Mn(II), Ni(II), Mg(II), Fe(II), Ti(II), V(II),Cr(III)-X, Co(III)-X, Ni(III)-X, Mn(III)-X, Fe(III)-X, Ca(II), Ge(II),AI(III)-X, Ti(III)-X, V(III)-X, Ge(IV)-(X)₂ or Ti(IV)-(X)₂; R₁ and R₂are independently selected from hydrogen, halide, a nitro group, anitrile group, an imine, an amine, an ether group, a silyl group, asilyl ether group, a sulfoxide group, a sulfonyl group, a sulfinategroup or an acetylide group or an optionally substituted alkyl, alkenyl,alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy, alkylthio,arylthio, alicyclic or heteroalicyclic group; R_(3A) and R_(3B) areindependently selected from optionally substituted alkylene, alkenylene,alkynylene, heteroalkylene, heteroalkenylene, heteroalkynylene, arylene,heteroarylene or cycloalkylene, wherein alkylene, alkenylene,alkynylene, heteroalkylene, heteroalkenylene and heteroalkynylene, mayoptionally be interrupted by aryl, heteroaryl, alicyclic orheteroalicyclic; R₅ is independently selected from H, or optionallysubstituted aliphatic, heteroaliphatic, alicyclic, heteroalicyclic,aryl, heteroaryl, alkylheteroaryl or alkylaryl; E₁ is C, E₂ is O, S orNH or E₁ is N and E₂ is O; E₃, E₄, E₅ and E₆ are each independentlyselected from N, NR₄, O and S, wherein when any of E₃, E₄, E₅ or E₆ areN,

is

, and wherein when any of E₃, E₄, E₅ or E₆ are NR₄, O or S,

is

; R₄ is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl; X is independently selectedfrom OC(O)R^(x), OSO₂R^(x), OSOR^(x), OSO(R^(x))₂, S(O)R^(x), OR^(x),phosphinate, halide, nitrate, hydroxyl, carbonate, amino, amido oroptionally substituted aliphatic, heteroaliphatic, alicyclic,heteroalicyclic, aryl or heteroaryl; R_(x) is independently hydrogen, oroptionally substituted aliphatic, haloaliphatic, heteroaliphatic,alicyclic, heteroalicyclic, aryl, alkylaryl or heteroaryl; and G isabsent or independently selected from a neutral or anionic donor ligandwhich is a Lewis base; and wherein: i) R_(3A) is different from R_(3B);and/or ii) At least one occurrence of E₃, E₄, E₅ and E₆ is different toa remaining occurrence of E₃, E₄, E₅ and E₆.
 2. The catalyst of claim 1,wherein R_(3A) is different from R_(3B), and each occurrence of E₃, E₄,E₅ and E₆ is the same.
 3. The catalyst of claim 1, wherein R_(3A) is thesame as R_(3B) and at least one occurrence of E₃, E₄, E₅ and E₆ isdifferent to a remaining occurrence of E₃, E₄, E₅ and Ee.
 4. Thecatalyst of claim 1, wherein R_(3A) is different from R₃₆ and at leastone occurrence of E₃, E₄, E₅ and E₆ is different to a remainingoccurrence of E₃, E₄, E₅ and E₆.
 5. The catalyst of claim 1, wherein E₃and E₅ are the same, and E₄ and E₆ are the same, and wherein E₃ and E₅are different from E₄ and E₆.
 6. The catalyst of claim 1, wherein E₃ andE₄ are the same, and E₅ and E₆ are the same, and wherein E₃ and E₄ aredifferent from E₅ and E₆.
 7. The catalyst of claim 1, wherein R_(3A) orR_(3B) is selected from substituted or unsubstituted alkylene,substituted or unsubstituted cycloalkylene or optionally substitutedarylene.
 8. The catalyst of claim 1, wherein R_(3A) is different fromR_(3B), R_(3A) is substituted or unsubstituted alkylene.
 9. The catalystof claim 1, wherein R_(3A) is different from R_(3B) and wherein R_(3A)is 2,2-dimethylpropylene and R_(3B) is phenylene, or R_(3A) is adisubstituted cycloalkylene which acts as a bridging group between twonitrogen centers in the catalyst of formula (I) and R_(3B) is2,2-dimethylpropylene, or R_(3A) is 2,2-dimethylpropylene and R_(3B) ispropylene or ethylene, or R_(3A) is propylene, and R₃₈ is2,2-dimethylpropylene.
 10. The catalyst of claim 1, wherein each E₃, E₄,E₅ and E₆ is NR₄, and one of the R₄ groups is different.
 11. Thecatalyst of claim 1, wherein each ES, E₄, E₅ and E₆ is NR₄, and two ofthe R₄ groups are different.
 12. The catalyst of claim 1, wherein two ofE₃, E₄, E₅ and E₆ are NR₄, and two of E₃, E₄, E₅ and E₆ are N.
 13. Thecatalyst of claim 1, wherein two of E₃, E₄, E₅ and E₆ are S, and two ofE₃, E₄, E₅ and E₆ are NR₄.
 14. The catalyst of claim 1, wherein eachoccurrence of R₂ and R₅ are H, E₁ is C and E₂ is O, S or NH.
 15. Thecatalyst of claim 1, wherein M₁ or M₂ is selected from Mg(II), Ni(II),Ni(III)-X, Co(II), Co(III)-X and Zn(II).
 16. The catalyst of claim 1,wherein M₁ or M₂ is selected from Ni(II) or Mg(II).
 17. The catalyst ofclaim 1, wherein M₁ and M₂ are the same.
 18. The catalyst of claim 1,wherein M₁ and M₂ are the same and are Ni(II) or Mg(III).
 19. Thecatalyst of claim 1, wherein M₁ and M₂ are the same and are Ni(II), andeach E₃, E₄, E₅ and E₆ is NR₄, wherein at least one of the R₄ groups isdifferent from a remaining occurrence of R₄ and is selected from anoptionally substituted alkyl or heteroalkyl.
 20. The catalyst accordingto claim 1, wherein R₁ is independently selected from hydrogen, halide,amino, nitro, sulfoxide, sulfonyl, sulfinate, and optionally substitutedalkyl, alkenyl, aryl, heteroaryl, alkoxy or alkylthio.
 21. The catalystof claim 1, wherein each occurrence of R₁ is the same.
 22. The catalystaccording to claim 1, wherein X is independently OC(O)R^(x), OSO₂R^(x),OS(O)R^(x), OSO(R^(x))₂, S(O)R^(x), OR^(x), halide, nitrate, hydroxyl,carbonate, amino, nitro, amido, and optionally substituted alkyl,heteroalkyl, aryl or heteroaryl.
 23. The catalyst according to claim 1,wherein R^(x) is independently optionally substituted alkyl, alkenyl,alkynyl, heteroalkyl, aryl, heteroaryl or alkylaryl.
 24. The catalyst ofclaim 1, wherein both occurrences of R₁ are the same, and are selectedfrom hydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate,silyl, silyl ether and an optionally substituted alkyl, alkenyl, aryl,heteroaryl, alkoxy, aryloxy or alkylthio; R₂ is hydrogen; R_(3A) andR_(3B) are the same or different, and are selected from substituted orunsubstituted alkylene, substituted or unsubstituted cycloalkylene andsubstituted or unsubstituted arylene; E₃ to E₆ are the same or differentand are selected from NR₄, S, N or O; R₄ is hydrogen, an optionallysubstituted alkyl or heteroalkyl; each X is the same, and is selectedfrom OC(O)R^(x), OR^(x), halide, carbonate, amino, nitro, alkyl, aryl,heteroaryl, phosphinate or OSO₂R^(x), R^(x) is alkyl, alkenyl, alkynyl,heteroalkyl, aryl, heteroaryl or alkylaryl; each G, where present, isindependently selected from halide; water; a heteroaryl optionallysubstituted by alkyl, alkenyl, alkynyl, alkoxy, halogen, hydroxyl, nitroor nitrile; M₁ and M₂ are independently selected from Mg(II), Zn(II),Ni(II), Ni(III)-X, Cr(II), Cr(III)-X, Co(II), Co(III)-X Mn(II), Fe(II),and Fe(II)-X.
 25. The catalyst of claim 1, wherein both occurrences ofR₁ are the same, and are selected from hydrogen, halide, amino, nitro,sulfoxide, sulfonyl, sulfinate, silyl, silyl ether and an optionallysubstituted alkyl, alkenyl, aryl, heteroaryl, alkoxy, aryloxy oralkylthio; R₂ is hydrogen; R_(3A) is a substituted or unsubstitutedcycloalkylene or alkylene and R_(3B) is a substituted or unsubstitutedalkylene, or arylene; each occurrence of E₃ to E₆ is NR₄; R₄ ishydrogen; each X is the same, and is selected from OC(O)R^(x), OR^(x),halide, carbonate, amino, nitro, alkyl, aryl, heteroaryl, phosphinate orOSO₂R^(x), R^(x) is alkyl, alkenyl, alkynyl, heteroalkyl, aryl,heteroaryl or alkylaryl; each G, where present, is independentlyselected from halide; water; a heteroaryl optionally substituted byalkyl, alkenyl, alkynyl, alkoxy, halogen, hydroxyl, nitro or nitrile; M₁and M₂ are independently selected from Mg(II), Zn(II), Ni(II), Ni(II)-X,Cr(II), Cr(III)-X, Co(II), Co(III)-X, Mn(II), Fe(II), and Fe(III)-X. 26.The catalyst of claim 1, wherein both occurrences of R₁ are the same,and are selected from hydrogen, halide, amino, nitro, sulfoxide,sulfonyl, sulfinate, silyl, silyl ether and an optionally substitutedalkyl, alkenyl, aryl, heteroaryl, alkoxy, aryloxy or alkylthio; R₂ ishydrogen; R_(3A) and R_(3B) are the same and are substituted orunsubstituted alkylene; each of E₃, E₄, E₅ and E₆ is NR₄ wherein one ofthe R₄ groups is different and selected from an optionally substitutedalkyl or heteroalkyl and the remaining R₄ groups are hydrogen; each X isthe same, and is selected from OC(O)R^(x), OR^(x), halide, carbonate,amino, nitro, alkyl, aryl, heteroaryl, phosphinate or OSO₂R, R^(x) isalkyl, alkenyl, alkynyl, heteroalkyl, aryl, heteroaryl or alkylaryl;each G, where present, is independently selected from halide; water; aheteroaryl optionally substituted by alkyl, alkenyl, alkynyl, alkoxy,halogen, hydroxyl, nitro or nitrile; M1 and M2 are independentlyselected from Mg(II), Zn(II), Cr(II), Cr(III)-X, Co(II), Co(III)-X,Mn(II), Ni(II), Ni(II)-X, Fe(III), and Fe(III)-X.
 27. The catalyst ofclaim 1, wherein both occurrences of R₁ are the same, and are selectedfrom hydrogen, halide, amino, nitro, sulfoxide, sulfonyl, sulfinate,silyl, silyl ether and an optionally substituted alkyl, alkenyl, aryl,heteroaryl, alkoxy, aryloxy or alkylthio; R₂ is hydrogen; R_(3A) andR_(3B) are selected from substituted or unsubstituted alkylene,substituted or unsubstituted cycloalkylene and substituted orunsubstituted arylene; E₃ to E₆ are selected from N, NR₄, S or O; R₄ isselected from hydrogen, or optionally substituted alkyl or heteroalkyl;each X is the same, and is selected from OC(O)R^(x), OR^(x), or OSO₂R,R^(x) is alkyl, alkenyl, alkynyl, heteroalkyl, aryl, heteroaryl oralkylaryl; each G, where present, is independently selected from halide;water; a heteroaryl optionally substituted by alkyl, alkenyl, alkynyl,alkoxy, halogen, hydroxyl, nitro or nitrile; M₁ and M₂ are independentlyselected from Mg(II), Zn(II), Cr(III), Cr(III)-X, Co(II), Co(III)-X,Mn(II), Ni(II), Ni(III)-X, Fe(II), and Fe(III)-X, ) and wherein: (i)R_(3A) is different from R_(3B); and/or (ii) at least one occurrence ofE₃, E₄, E₅ and E₆ is different to a remaining occurrence of E₃, E₄, E₅and E₆.
 28. The catalyst of claim 1, wherein both occurrences of R₁ arethe same, and are selected from an optionally substituted alkyl; R₂ ishydrogen; R_(3A) and R_(3B) are selected from substituted orunsubstituted alkylene, substituted or unsubstituted cycloalkylene, andsubstituted or unsubstituted arylene; each occurrence of E₃ to E₆ isNR₄; R₄ is selected from hydrogen, or optionally substituted alkyl orheteroalkyl; each X is the same, and is selected from OC(O)R^(x),OR^(x), or OSO₂R^(x), R^(x) is alkyl, alkenyl, alkynyl, heteroalkyl,aryl, heteroaryl or alkylaryl; M₁ and M₂ are independently selected fromMg(II), Ni(III), Ni(III)-X Co(II), Co(III)-X and Zn(II), and wherein:(i) R_(3A) is different from R_(3B); and/or (ii) at least one occurrenceof E₃, E₄, E₅ and E₆ is different to a remaining occurrence of E₃, E₄,E₅ and E₆.
 29. The catalyst of claim 1, wherein both occurrences of R₁are the same, and are tertiary butyl; R₂ is hydrogen; R_(3A) and R_(3B)are selected from tertiary butylene, benzylene, ethylene, propylene,2,2-dimethylpropylene; each occurrence of E₃ to E₆ is NR₄; R₄ isselected from hydrogen, methyl, ethyl, propyl, butyl, or-alkyl-C(O)—OR₁₉; each X is the same, and is OAc; M₁ and M₂ areindependently selected from Mg(II), Ni(II), Co(II), Co(III)-X, Ni(III)-Xand Zn(II), and wherein: iii) R_(3A) is different from R_(3B); and/oriv) at least one occurrence of E₃, E₄, E₅ and E₆ is different to aremaining occurrence of E₃, E₄, E₅ and E₆.
 30. The catalyst of claim 1,of the formula:


31. The catalyst of claim 1 of the formula:


32. A ligand of formula (II):

wherein: R₁ and R₂ are independently selected from hydrogen, halide, anitro group, a nitrile group, an imine, an amine, an ether group, asilyl group, a silyl ether group, a sulfoxide group, a sulfonyl group, asulfinate group or an acetylide group or an optionally substitutedalkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy,alkylthio, arylthio, alicyclic or heteroalicyclic group; R_(3A) andR_(3B) are independently selected from optionally substituted alkylene,alkenylene, alkynylene, heteroalkylene, heteroalkenylene,heteroalkynylene, arylene, heteroarylene or cycloalkylene, whereinalkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene andheteroalkynylene, may optionally be interrupted by aryl, heteroaryl,alicyclic or heteroalicyclic; R₅ is independently selected from H, oroptionally substituted aliphatic, heteroaliphatic, alicyclic,heteroalicyclic, aryl, heteroaryl, alkylheteroaryl or alkylaryl; E₁ isC, E₂ is OY, S or NH or E₁ is N and E₂ is OY; Y is hydrogen or an alkalimetal; E₃, E₄, E₅ and E₆ are each independently selected from N, NR₄, Oand S, wherein when any of E₃, E₄, E₅ or E₆ are N,

is

, and wherein when any of E₃, E₄, E₅ or E₆ are NR₄, O or S,

is

; R₄ is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl; and wherein: (i) R_(3A) isdifferent from R_(3B); and/or (ii) at least one occurrence of E₃, E₄, E₅and E₆ is different to a remaining occurrence of E₃, E₄, E₅ and E₆. 33.The ligand of claim 32, wherein both occurrences of R, are the same, andare selected from hydrogen, halide, amino, nitro, sulfoxide, sulfonyl,sulfinate, silyl, silyl ether and an optionally substituted alkyl,alkenyl, aryl, heteroaryl, alkoxy, aryloxy or alkylthio; R₂ is hydrogen;R_(3A) and R_(3B) are selected from substituted or unsubstitutedalkylene, substituted or unsubstituted cycloalkylene and substituted orunsubstituted arylene; E₃ to E₆ are N, NR₄, S or O; R₄ is selected fromhydrogen, or optionally substituted alkyl or heteroalkyl; and wherein:i) R_(3A) is different from R_(3B); and/or ii) at least one occurrenceof E₃, E₄, E₅ and E₆ is different to a remaining occurrence of E₃, E₄,E₅ and E₆.
 34. The ligand of claim 32 wherein both occurrences of R₁ arethe same, and are selected from an optionally substituted alkyl; R₂ ishydrogen; R_(3A) and R₃, are selected from substituted or unsubstitutedalkylene, substituted or unsubstituted cycloalkylene, and substituted orunsubstituted arylene; each occurrence of E₃ to E₆ is NR₄; R₄ isselected from hydrogen, or optionally substituted alkyl or heteroalkyl;and wherein: iii) R_(3A) is different from R_(3B); and/or iv) at leastone occurrence of E₃, E₄, E₅ and E₆ is different to a remainingoccurrence of E₃, E₄, E₅ and E₆.
 35. The ligand of claim 32, whereinboth occurrences of R₁ are the same, and are tertiary butyl; R₂ ishydrogen; R_(3A) and R₃, are selected from butylene, benzylene,ethylene, propylene, 2,2-dimethylpropylene; each occurrence of E₃ to E₆is NR₄; R₄ is selected from hydrogen, methyl, ethyl, propyl, butyl, or-alkyl-C(O)—OR₁₉; and wherein: i) R_(3A) is different from R_(3B);and/or ii) at least one occurrence of E₃, E₄, E₅ and E₆ is different toa remaining occurrence of E₃, E₄, E₅ and E₆.
 36. The ligand of claim 32of the formula:

wherein: R₁ is tertiary butyl; R₂ is hydrogen; R₃ is2,2-dimethylpropylene; and R₄ is selected from methyl, ethyl, propyl, orbutyl; or:

wherein: R₃ is selected from 2,2-dimethylpropylene, propylene, orethylene; or:

wherein: R is methyl or hydrogen; or:

wherein: R₁ is tertiary butyl; R₂ is hydrogen; R₃ is2,2-dimethylpropylene; and R₄ is methyl, ethyl, propyl, or butyl. 37.The ligand of claim 32, wherein the ligand comprises at least oneN-substituent, and is selected from:

wherein: R₁ is tertiary butyl; R₂ is hydrogen; R₃ is2,2-dimethylpropylene; and R₄ is selected from methyl, ethyl, propyl, orbutyl; or

wherein R₁ is tertiary butyl; R₂ is hydrogen; R₃ is2,2-dimethylpropylene; and R₄ is methyl, ethyl, propyl, or butyl.
 38. Aprocess of asymmetric N-substitution of a symmetrical ligand having atetraaminophenol coordination sphere, the process comprising thefollowing steps: c) Protecting at least two of the amino groups of thecoordination sphere of the symmetrical ligand with an optionallysubstituted alkylene; d) asymmetrically N-substituting one or more ofthe protected amino groups of the product of step (a) with asubstituent.
 39. The process according to claim 39, wherein step (a)comprises reacting the symmetrical ligand with a protecting reagentcomprising an optionally substituted alkylene group.
 40. The processaccording to claim 39, wherein step (a) comprises protecting the aminogroups of the coordination sphere of the symmetrical ligand by formingbridging groups between the adjacent amino groups or amino and phenolicgroups.
 41. The process according to claim 39, wherein step (b)comprises asymmetrically N-substituting one or more of the protectedamino groups of the product of step (a) with an N-substituting agent.42. The process according to claim 42, wherein the N-substituting agentis an alkylating agent or an alkene.
 43. The process according to claim39, wherein the process further comprises step (c) hydrolysing theoptionally substituted alkylene bridging groups between the adjacentamino groups.
 44. The process according to claim 39, wherein theasymmetrical ligand is formula (II):

wherein: R₁ and R₂ are independently selected from hydrogen, halide, anitro group, a nitrile group, an imine, an amine, an ether group, asilyl group, a silyl ether group, a sulfoxide group, a sulfonyl group, asulfinate group or an acetylide group or an optionally substitutedalkyl, alkenyl, alkynyl, haloalkyl, aryl, heteroaryl, alkoxy, aryloxy,alkylthio, arylthio, alicyclic or heteroalicyclic group; R_(3A) andR_(3B) are independently selected from optionally substituted alkylene,alkenylene, alkynylene, heteroalkylene, heteroalkenylene,heteroalkynylene, arylene, heteroarylene or cycloalkylene, whereinalkylene, alkenylene, alkynylene, heteroalkylene, heteroalkenylene andheteroalkynylene, may optionally be interrupted by aryl, heteroaryl,alicyclic or heteroalicyclic; R₅ is independently selected from H, oroptionally substituted aliphatic, heteroaliphatic, alicyclic,heteroalicyclic, aryl, heteroaryl, alkylheteroaryl or alkylaryl; E₁ isC, E₂ is OY, S or NH or E₁ is N and E₂ is OY; Y is hydrogen or an alkalimetal; E₃, E₄, E₅ and E₆ are each independently selected from N, NR₄, Oand S, wherein when any of E₃, E₄, E₅ or E₆ are N,

is

, and wherein when any of E₃, E₄, E₅ or E₆ are NR₄, O or S,

is

; R₄ is independently selected from H, or optionally substitutedaliphatic, heteroaliphatic, alicyclic, heteroalicyclic, aryl,heteroaryl, alkylheteroaryl or alkylaryl; and wherein: (i) R_(3A) isdifferent from R_(3B); and/or (ii) at least one occurrence of E₃, E₄, E₅and E₆ is different to a remaining occurrence of E₃, E₄, E₅ and E₆, andwherein the ligand comprises at least one N-substituent, and is selectedfrom:

wherein: R₁ is tertiary butyl; R₂ is hydrogen; R₃ is2,2-dimethylpropylene; and R₄ is selected from methyl, ethyl, propyl, orbutyl; or

wherein R₁ is tertiary butyl; R₂ is hydrogen; R₃ is2,2-dimethylpropylene; and R₄ is methyl, ethyl, propyl, or butyl.
 46. Aprocess for the reaction of: (i) carbon dioxide with an epoxide; (ii) anepoxide and an anhydride; and/or (iii) a lactide and/or a lactone, inthe presence of the catalyst of claim 1, optionally wherein the processis carried out in the presence of a chain transfer agent.
 47. Theprocess of claim 46, wherein the process is carried out in a continuousflow reactor, or a batch reactor.
 48. The process of claim 47, whereinthe reaction is carried out in a continuous flow reactor.